AQA GCE Biology
3.2.1 Cell structure
The cell theory is a unifying concept in biology.
18.104.22.168 Structure of eukaryotic cells
The structure of eukaryotic cells, restricted to the structure and function of: cell-surface membrane, nucleus (containing chromosomes, consisting of protein-bound, linear DNA, and one or more nucleoli), mitochondria, chloroplasts (in plants and algae), Golgi apparatus and Golgi vesicles, lysosomes (a type of Golgi vesicle that releases lysozymes), ribosomes, rough endoplasmic reticulum and smooth endoplasmic reticulum, cell wall (in plants, algae and fungi), cell vacuole (in plants).
In complex multicellular organisms, eukaryotic cells become specialised for specific functions.
Specialised cells are organised into tissues, tissues into organs and organs into systems. Students should be able to apply their knowledge of these features in explaining adaptations of eukaryotic cells.
22.214.171.124 Structure of prokaryotic cells and of viruses
Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in having: cytoplasm that lacks membrane-bound organelles, smaller ribosomes, no nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins, a cell wall that contains murein, a glycoprotein.
In addition, many prokaryotic cells have: one or more plasmids, a capsule surrounding the cell, one or more flagella. Details of these structural differences are not required.
Viruses are acellular and non-living. The structure of virus particles to include genetic material, capsid and attachment protein.
126.96.36.199 Methods of studying cells
The principles and limitations of optical microscopes, transmission electron microscopes and scanning electron microscopes.
Measuring the size of an object viewed with an optical microscope.
The difference between magnification and resolution.
3.2.2 All cells arise from other cells
Within multicellular organisms, not all cells retain the ability to divide.
Eukaryotic cells that do retain the ability to divide show a cell cycle. DNA replication occurs during the interphase of the cell cycle.
Mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication. The behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis. The role of spindle fibres attached to centromeres in the separation of chromatids. Division of the cytoplasm (cytokinesis) usually occurs, producing two new cells.
Students should be able to: recognise the stages of the cell cycle: interphase, prophase, metaphase, anaphase and telophase (including cytokinesis), explain the appearance of cells in each stage of mitosis. Mitosis is a controlled process.
Uncontrolled cell division can lead to the formation of tumours and of cancers. Many cancer treatments are directed at controlling the rate of cell division.
Binary fission in prokaryotic cells involves: replication of the circular DNA and of plasmids, division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.
3.2.3 Transport across cell membranes
The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes, is the same.
The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model of membrane structure. Cholesterol may also be present in cell membranes where it restricts the movement of other molecules making up the membrane.
Movement across membranes occurs by: simple diffusion (involving limitations imposed by the nature of the phospholipid bilayer), facilitated diffusion (involving the roles of carrier proteins and channel proteins), osmosis (explained in terms of water potential), active transport (involving the role of carrier proteins and the importance of the hydrolysis of ATP), co-transport (illustrated by the absorption of sodium ions and glucose by cells lining the mammalian ileum). Cells may be adapted for rapid transport across their internal or external membranes by an increase in surface area of, or by an increase in the number of protein channels and carrier molecules in, their membranes.
3.8.2 Gene expression is controlled by a number of features
Totipotent cells are cells that can mature into any type of body cell. During development, totipotent cells translate only part of their DNA, resulting in cell specialisation. Totipotent cells occur only for a limited time in mammalian embryos.
Pluripotent, multipotent and unipotent cells are found in mature mammals. They can divide to form a limited number of different cell types. Pluripotent stem cells can divide in unlimited numbers and can be used in treating human disorders.
Unipotent cells, exemplified by cardiomycetes. Induced pluripotent stem cells (iPS cells) can be produced from unipotent cells using appropriate protein transcription factors.
Students should be able to evaluate the use of stem cells in treating human disorders.
Edexcel GCE Biology A (Salters-Nuffield)
Topic 2 Genes and Health
2.2 (i) Know the structure and properties of cell membranes.
(ii) Understand how models such as the fluid mosaic model of cell membranes are interpretations of data used to develop scientific explanations of the structure and properties of cell membranes.
2.3 Understand what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane (consideration of water potential is not required).
2.4 (i) Understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis.
(ii) Understand the involvement of carrier and channel proteins in membrane transport.
Topic 3: Voice of the Genome
3.1 Know that all living organisms are made of cells, sharing some common features.
3.2 Know the ultrastructure of eukaryotic cells, including nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, and Golgi apparatus.
3.3 Understand the role of the rough endoplasmic reticulum (rER) and the Golgi apparatus in protein transport within cells, including their role in the formation of extracellular enzymes.
3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA.
3.5 Be able to recognise the organelles in 3.2 from electron microscope (EM) images.
3.9 Understand the role of meiosis in ensuring genetic variation through the production of non-identical gametes as a consequence of independent assortment of chromosomes and crossing over of alleles between chromatids (details of the stages of meiosis are not required).
3.10 Understand the role of mitosis and the cell cycle in producing identical daughter cells for growth and asexual reproduction.
3.11 (i) Understand what is meant by the terms ‘stem cell, pluripotency and totipotency’.
(ii) Be able to discuss the way society uses scientific knowledge to make decisions about the use of stem cells in medical therapies.
3.12 Understand how cells become specialised through differential gene expression, producing active mRNA leading to synthesis of proteins, which in turn control cell processes or determine cell structure in animals and plants, including the lac operon.
3.13 Understand how the cells of multicellular organisms are organised into tissues, tissues into organs and organs into systems.
Edexcel GCE Biology B
Topic 1: Biological molecules
iv. Understand how the structure and properties of phospholipids relate to their function in cell membranes.
Topic 2: Cells, Viruses and Reproduction of Living Things
2.1 Eukaryotic and prokaryotic cell structure and function
(i) Understand that cell theory is a unifying concept that states that cells are a fundamental unit of structure, function and organisation in all living organisms.
(ii) Understand that in complex organisms, cells are organised into tissues, organs, and organ systems.
(iii) Know the ultrastructure of prokaryotic cells and the structure of organelles, including: nucleoid, plasmids, 70S ribosomes and cell wall. iii. Know the ultrastructure of eukaryotic cells and the functions of organelles, including: nucleus, nucleolus, 80S ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, Golgi apparatus, cell wall, chloroplasts, vacuole and tonoplast.
(iv) Know how magnification and resolution can be achieved using light and electron microscopy.
2.3 Eukaryotic cell cycle and division
(i) Know that the cell cycle is a regulated process in which cells divide into two identical daughter cells, and that this process consists of three main stages: interphase, mitosis and cytokinesis.
(ii) Understand what happens to genetic material during the cell cycle, including the stages of mitosis.
(iii) Understand how mitosis contributes to growth, repair and asexual reproduction.
(iv) Understand how meiosis results in haploid gametes, including the stages of meiosis.
(v) Understand that meiosis results in genetic variation through recombination of alleles, including independent assortment and crossing over.
Topic 4: Exchange and Transport
4.2 Cell transport mechanisms
(i) Know the structure of the cell surface membrane with reference to the fluid mosaic model.
(ii) Understand how passive transport is brought about by: diffusion, facilitated diffusion (through carrier proteins and protein channels) and osmosis.
(iii) Understand how the properties of molecules affects how they are transported, including solubility, size and charge.
(iv) Know that large molecules can be transported into and out of cells through theformation of vesicles, in the processes of endocytosis and exocytosis.
(v) Understand the process of active transport, including the role of ATP
Topic 7: Modern Genetics
7.2 Factors affecting gene expression
(i) Know that transcription factors are proteins that bind to DNA.
(ii) Understand the role of transcription factors in regulating gene expression.
(v) Know that epigenetic modification is important in ensuring cell differentiation
7.3 Stem cells
(i) Understand what is meant by a stem cell, including the differences between totipotent, pluripotent and multipotent stem cells.
(ii) Understand that pluripotent stem cells from embryos provide opportunities to develop new medical advances although there are ethical considerations.
(iii) Understand how epigenetic modifications can result in totipotent stem cells in the embryo developing into pluripotent cells in the blastocyst and finally into fully differentiated somatic cells.
(iv) Understand how differentiated fibroblasts can be reprogrammed to form induced pluripotent stem cells (iPS cells) by the artificial introduction of named genes.
(v) Understand why the use of iPS stem cells may be less problematic than the use of embryonic stem cells.
Topic 8: Origins of Genetic Variation
8.1 Origins of genetic variation
(i) Understand that mutations are the source of new variations and that the processes of random assortment and crossing over during meiosis give rise to new combinations of alleles in gametes.
Topic 9: Control Systems
9.2 Chemical control in mammals
(ii) Know that there are two main modes of action in hormones: hormones attach to receptor sites and trigger the release of a second messenger that activates specific enzymes in the cell, including adrenaline; hormones enter cells and bind directly to transcription factors, including oestrogen.
OCR GCE Biology A
2.1.1 Cell structure
(a) the use of microscopy to observe and investigate different types of cell and cell structure in a range of eukaryotic organisms
(b) the preparation and examination of microscope slides for use in light microscopy. To include an appreciation of the images produced by a range of microscopes, light microscope, transmission electron microscope, scanning electron microscope and laser scanning confocal microscope.
(c) the use of staining in light microscopy. To include the use of differential staining to identify different cellular components and cell types.
(d) the representation of cell structure as seen under the light microscope using drawings and annotated diagrams of whole cells or cells in sections of tissue
(e) the use and manipulation of the magnification formula
(f) the difference between magnification and resolution. To include an appreciation of the differences in resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope.
(g) the ultrastructure of eukaryotic cells and the functions of the different cellular components. To include the following cellular components and an outline of their functions: nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum (ER), Golgi apparatus, ribosomes, mitochondria, lysosomes, chloroplasts, plasma membrane, centrioles, cell wall, flagella and cilia.
(h) photomicrographs of cellular components in a range of eukaryotic cells. To include interpretation of transmission and scanning electron microscope images.
(i) the interrelationship between the organelles involved in the production and secretion of proteins
(j) the importance of the cytoskeleton. To include providing mechanical strength to cells, aiding transport within cells and enabling cell movement.
(k) the similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells.
2.1.5 Biological membranes
(a) the roles of membranes within cells and at the surface of cells. To include the roles of membranes as; partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles; sites of chemical reactions; sites of cell communication (cell signalling).
(b) the fluid mosaic model of membrane structure and the roles of its components. To include phospholipids, cholesterol, glycolipids, proteins and glycoproteins AND the role of membrane-bound receptors as sites where hormones and drugs can bind.
(c) (i) factors affecting membrane structure and permeability
(ii) practical investigations into factors affecting membrane structure and permeability. To include the effects of temperature and solvents.
(d) (i) the movement of molecules across membranes/ practical investigations into the factors affecting diffusion rates in model cells . To include diffusion and facilitated diffusion as passive methods AND active transport, endocytosis and exocytosis as processes requiring adenosine triphosphate (ATP) as an immediate source of energy.
(e) (i) the movement of water across membranes by osmosis and the effects that solutions of different water potential can have on plant and animal cells. Osmosis to be explained in terms of a water potential gradient across a partially-permeable membrane.
(ii) practical investigations into the effects of solutions of different water potential on plant and animal cells.
2.1.6 Cell division, cell diversity and cellular organisation
(a) the cell cycle. To include the processes taking place during interphase (G1, S and G2), mitosis and cytokinesis, leading to genetically identical cells.
(b) how the cell cycle is regulated. To include an outline of the use of checkpoints to control the cycle.
(c) the main stages of mitosis. To include the changes in the nuclear envelope, chromosomes, chromatids, centromere, centrioles, spindle fibres and cell membrane.
(e) the significance of mitosis in life cycles. To include growth, tissue repair and asexual reproduction in plants, animals and fungi.
(f) the significance of meiosis in life cycles. To include the production of haploid cells and genetic variation by independent assortment and crossing over.
(g) the main stages of meiosis. To include interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, prophase 2, metaphase 2, anaphase 2, telophase 2 (no details of the names of the stages within prophase 1 are required) and the term homologous chromosomes.
(h) how cells of multicellular organisms are specialised for particular functions. To include erythrocytes, neutrophils, squamous and ciliated epithelial cells, sperm cells, palisade cells, root hair cells and guard cells. (i) the organisation of cells into tissues, organs and organ systems.
(j) the features and differentiation of stem cells. To include stem cells as a renewing source of undifferentiated cells. (m) the potential uses of stem cells in research and medicine. To include the repair of damaged tissues, the treatment of neurological conditions such as Alzheimer’s and Parkinson’s, and research into developmental biology.
5.1.1 Communication and homeostasis
(b) the communication between cells by cell signalling. To include signalling between adjacent cells and signalling between distant cells.
6.1.1 Cellular Control
(d) the importance of mitosis and apoptosis as mechanisms controlling the development of body form. To include an appreciation that the genes which regulate the cell cycle and apoptosis are able to respond to internal and external cell stimuli e.g. stress.
OCR GCE Biology B
2.1.1 Cells and microscopy
(a)(i) the importance of microscopy in the development of the cell theory as a unifying concept in biology and the investigation of cell structure. To include the use of the light microscope, transmission and scanning electron microscopes and recent developments such as the confocal scanning microscope .
(g) the ultrastructure of a typical eukaryotic animal cell, such as a leucocyte, as revealed by an electron microscope. To include the structure and function of the following: plasma membrane, Golgi apparatus, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER), ribosomes, lysosomes, vesicles, mitochondria, cytoskeleton, centrioles, nucleus and nucleolus.
(h)(ii) the similarities and differences between the structure of eukaryotic and prokaryotic cells.
(j) how the plasma membrane is composed of modified lipids and how the structure of triglycerides and phospholipids is related to their functions. To include reference to fatty acids, glycerol, phosphate groups, ester bonds and hydrophobic/hydrophilic properties
(k) the fluid mosaic model of the typical plasma membrane. To include the location and function of phospholipids, intrinsic proteins, extrinsic proteins, cholesterol, glycolipids and glycoproteins.
(l) the movement of molecules across plasma membranes. To include diffusion and facilitated diffusion as passive methods of transport across membranes AND active transport, endocytosis and exocytosis as processes requiring ATP as an immediate source of energy. (n) the roles of membranes within and at the surface of cells
(o) the interrelationship between the organelles involved in the production and secretion of proteins. To include the role of the cytoskeleton and motor proteins, the nucleus, ribosomes, RER, Golgi and vesicles (no details of transcription and translation are required at this stage).
3.1.1 The developing cell: cell division and cell differentiation
(a) the cell cycle. To include the processes taking place during interphase (G1,S and G2), mitosis and cytokinesis, leading to genetically identical daughter cells.
(b) (i) the changes that take place in the nuclei and cells of animals and plants during mitosis. To include the changes in the nuclear envelope and the behaviour of the centrioles, spindle fibres, centromere, chromatids and chromosomes.
(ii) the microscopic appearance of cells undergoing mitosis.. To include the examination and drawing of stained sections or squashes of plant tissue and the identification of the stages observed.
(d) the importance of apoptosis and mitosis in growth and repair.
(e) (i) the differentiation of stem cells into specialised cells. To include an appreciation of the differences between totipotent, pluripotent and multipotent stem cells, and the differentiation of bone marrow stem cells into specialised blood cells.
(ii) current applications and uses of stem cells. To include the use of bone marrow stem cells.
3.1.2 The developing individual: meiosis, growth and development
(a) the significance of meiosis in sexual reproduction and the production of haploid gametes in plants and animals (b) the stages of meiosis in plant and animal cells. To include the use of diagrams to describe interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, prophase 2, metaphase 2, anaphase 2, telophase 2 (no details of the names of the stages within prophase 1 are required).
(c) how meiosis produces daughter cells that are genetically different. To include the importance of chiasma formation, crossing over, independent assortment of chromosomes (metaphase 1) and chromatids (metaphase 2), in producing genetic variation.
3.3.1 The cellular basis of cancer and treatment
(b) the cellular basis of cancer. To include an outline of cell cycle control and the changes in control which lead to the formation of tumours and metastases.
(d) how mutations to tumour suppressor genes can lead to cancer. To include the p53 gene.
SQA HIGHER BIOLOGY
DNA and the Genome
4. Cellular differentiation
(a) Cellular differentiation is the process by which a cell develops more specialised functions by expressing the genes characteristic for that type of cell.
Differentiation into specialised cells from meristems in plants; embryonic and tissue (adult) stem cells in animals.
(b) Embryonic and tissue (adult) stem cells.
Research and therapeutic uses of stem cells by reference to the repair of damaged or diseased organs or tissues. Stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work. Stem cells can be used as model cells to study how diseases develop or for drug testing. The ethical issues of stem cell use and the regulation of their use.
SQA ADVANCED HIGHER BIOLOGY
Cells and Proteins
The proteome is the entire set of proteins expressed by a genome. The proteome is larger than the number of genes due to alternative RNA splicing and post-translational modification. Not all genes are expressed as proteins in a particular cell.
( b) Protein structure, binding and conformational change
(ii) Hydrophobic and hydrophilic interactions influence the location of cellular proteins. The fluid mosaic model of membrane structure. Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral proteins within the phospholipid bilayer. Some integral proteins are transmembrane, for example channels, transporters and many receptors.
3. Membrane proteins
(a) Movement of molecules across membranes.
The phospholipid bilayer as a barrier to ions and most uncharged polar molecules. Some small molecules such as oxygen and carbon dioxide pass through. Specific transmembrane proteins, which act as channels or transporters, control ion concentrations and concentration gradients. To perform specialised functions, different cell types and different cell compartments have different channel and transporter proteins.
Passage of molecules through channel proteins is passive, eg aquaporin. Some channel proteins are gated and change conformation to allow or prevent diffusion, eg sodium channels, potassium channels. ‘Gated’ channels can be controlled by signal molecules (ligand-gated channels) or changes in ion concentrations (voltage-gated channels). Transporter proteins change conformation to transport molecules across a membrane. Transport can be facilitated, eg glucose symport or active, eg Na/KATPase. Conformational change in active transport requires energy from hydrolysis of ATP.
(b) Signal transduction.
Some cell surface receptor proteins convert an extracellular chemical signal to a specific intracellular response through a signal transduction pathway. This may result in the activation of an enzyme or G protein, a change in uptake or secretion of molecules, rearrangement of the cytoskeleton or activation of proteins that regulate gene transcription.
(c) Ion transport pumps and generation of ion gradients.
The sodium potassium pump transports ions against a steep concentration gradient using energy directly from ATP. The transporter protein has high affinity for sodium ions inside the cell; binding occurs; phosphorylation by ATP; conformation changes; affinity for ions changes; sodium ions released outside of the cell, potassium ions bind outside the cell; dephosphorylation; conformation changes; potassium ions taken into cell; affinity returns to start.
5. Communication within multicellular organisms
(a) Coordination Receptor molecules of target cells are proteins with a binding site for a specific signal molecule.
Binding changes the conformation of the receptor and this can alter the response of the cell. Different cell types produce specific signals which can only be detected and responded to by cells with the specific receptor. In a multicellular organism different cell types may show a tissue specific response to the same signal.
(b) Hydrophobic signals and control of transcription.
Hydrophobic signalling molecules can diffuse through membranes so their receptor molecules can be within the nucleus.
(c) Hydrophilic signals and transduction.
Hydrophilic signals require receptor molecules to be at the surface of the cell. Transmembrane receptors change conformation when the ligand binds on the cell surface; the signal molecule does not enter the cell but the signal is transduced across the membrane of the cell. Transduced hydrophilic signals often involve cascades of G-proteins or phosphorylation by kinase enzymes.
6. Protein control of cell division
(a) Cell division requires the remodelling of the cell’s cytoskeleton
The cytoskeleton gives mechanical support and shape to cells. The cytoskeleton consists of different types of proteins extending throughout the cytoplasm. Microtubules composed of hollow straight rods made of globular proteins called tubulins govern the location and movement of membrane-bound organelles and other cell components. Microtubules are found in all eukaryotic cells and radiate from the centrosome (the microtubule organising centre). Microtubules form the spindle fibres, which are active during cell division.
(b) The cell cycle
An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease. An uncontrolled increase in the rate of the cell cycle may result in tumour formation.
The cell cycle consists of interphase and mitosis. Interphase consists of an initial growth phase G1 followed by an S phase where the cell continues to grow and copies its chromosomes and a further G2 growth phase, in preparation for M phase (mitosis and cytokinesis). Mitosis is a dynamic continuum of sequential changes described as prophase, metaphase, anaphase and telophase. Role of spindle fibres in the movement of chromosomes on metaphase plate, separation of sister chromatids and formation of daughter nuclei. Cytokinesis is the separation of the cytoplasm into daughter cells.
WJEC GCE Biology
2. Cell structure and organisation
(a) the structure and function of the following: mitochondria; endoplasmic reticulum (rough and smooth); ribosomes; Golgi body; lysosomes; centrioles; chloroplasts; vacuoles; nucleus; chromatin; nuclear envelope; nucleolus; plasmodesmata
(b) the structure of prokaryotic cells and viruses
(c) cell theory and the similarities and differences in the cell structures of eukaryotes (animal and plant) and prokaryotes and of viruses, including the examination of a range of electron micrographs of prokaryote and eukaryote cells to show structure
(d) the levels of organisation including aggregation of cells into tissues, tissues into organs and organs into organ systems and also the examination of a range of prepared slides showing examples of epithelia, muscle and connective tissue
3. Cell membranes and transport
(a) the principal components of the plasma membrane and understand the fluid- mosaic model
(b) The factors affecting permeability of the plasma membrane
(c) the following transport mechanisms: diffusion and factors affecting the rate of diffusion; osmosis and water potential; pinocytosis; facilitated diffusion; phagocytosis; secretion (exocytosis); active transport and the influence of cyanide
2.2 Continuity of Life
2. Genetic information is copied and passed on to daughter cells
(a) interphase and the main stages of mitosis
(b) the significance of mitosis as a process in which daughter cells are provided with identical copies of genes and the process of cytokinesis
(c) the significance of mitosis in terms of damage and disease: repeated cell renewal, damage repair and healing and unrestricted division leading to cancerous growth
(d) the main stages of meiosis (names of subdivisions of prophase 1 not required) and cytokinesis
(e) the differences between mitosis and meiosis, including that mitosis produces genetically identical daughter cells whereas meiosis produces non-identical daughter cells
5. Application of reproduction and genetics
(a) the Human Genome Project and its extension to the 100K Genome Project
(i) the issues surrounding the use of stem cells for replacing damaged tissues and organs
International Baccalaureate Diploma Programme: Biology
Topic 1: Cell biology
1.1 Introduction to cells
According to the cell theory, living organisms are composed of cells.
Organisms consisting of only one cell carry out all functions of life in that cell. Surface area to volume ratio is important in the limitation of cell size. Multicellular organisms have properties that emerge from the interaction of their cellular components. Specialized tissues can develop by cell differentiation in multicellular organisms. Differentiation involves the expression of some genes and not others in a cell’s genome. The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
1.2 Ultrastructure of cells
Prokaryotes have a simple cell structure without compartmentalization.
Eukaryotes have a compartmentalized cell structure.
Electron microscopes have a much higher resolution than light microscope
1.3 Membrane structure
Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Membrane proteins are diverse in terms of structure, position in the membrane and function.
Cholesterol is a component of animal cell membranes.
1.4 Membrane transport
Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis.
Vesicles move materials within cells.
1.5 The origin of cells
Cells can only be formed by division of pre-existing cells.
The first cells must have arisen from non-living material.
The origin of eukaryotic cells can be explained by the endosymbiotic theory.
1.6 Cell division
Mitosis is division of the nucleus into two genetically identical daughter nuclei.
Chromosomes condense by supercoiling during mitosis. Cytokinesis occurs after mitosis and is different in plant and animal cells.
Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.
Cyclins are involved in the control of the cell cycle.
Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.
Topic 3: Genetics
Prokaryotes have one chromosome consisting of a circular DNA molecule.
Some prokaryotes also have plasmids but eukaryotes do not.
Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
Diploid nuclei have pairs of homologous chromosomes.
Haploid nuclei have one chromosome of each pair.
One diploid nucleus divides by meiosis to produce four haploid nuclei.
The halving of the chromosome number allows a sexual life cycle with fusion of gametes.
DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation.
Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number.
Crossing over and random orientation promotes genetic variation.
Fusion of gametes from different parents promotes genetic variation.
About this resource
This resource was first published in ‘The Cell’.