National 5 Biology: Cell Biology

Cell Ultrastructure
1. Cell Structure
  1. Animal
    1. Nucleus
    2. Cytoplasm
    3. Mitochondria
    4. Ribosome
    5. Cell Membrane
  2. Plant
    1. Ribosome
    2. Chloroplast
    3. Cytoplasm
    4. Cell Wall
    5. Mitochondria
    6. Vacuole
    7. Nucleus
    8. Cell Membrane
  3. Fungal
    1. Mitochondria
    2. Cell Wall
    3. Cytoplasm
    4. Nucleus
    5. Vacuole
    6. Cell Membrane
    7. Ribosome
  4. Bacterial
    1. Cell Wall
    2. Cell Membrane
    3. Plasmid
    4. Cytoplasm
    5. Ribosome
    6. Chromosome
2. Living Organisms and Cells
  1. Living organisms are made up of cells
  2. Unicellular
    1. Made up of only one cell
  3. Multicellular
    1. Made up of more than one cell
3. Functions of Cell Structures
  1. Mitochondria
    1. Site of ATP production in aerobic respiration
  2. Cell Wall
    1. Outer layer of cell
    2. Provides support
    3. Freely permeable
  3. Ribosome
    1. Site of protein synthesis
  4. Cyloplasm
    1. Contains organelles
    2. Site of chemical reactions
  5. Plasmid
    1. Circular ring of DNA
  6. Nucleus
    1. Contains genetic information and controls all cell activities
  7. Chloroplast
    1. Site of photosynthesis
      1. Produces carbohydrate
  8. Cell Membrane
    1. Controls the entry and exit of substances from the cell
    2. Selectively permeable
  9. Vacuole
    1. Provides support
    2. Stores a solution of water, salts and sugars
Transport Across Cell Membranes
1. Cell Membrane Structure
  1. Composed of proteins and phospholipids
  2. Proteins
    1. Found in a patchy arrangement, spread through the phospholipid molecules
    2. Some proteins form pores
      1. Allowing cell membranes to be selectively permeable
  3. Phospholipids
    1. Form a bi-layer which is in constant motion
  4. Selectively Permeable
    1. Small, soluble molecules pass easily through the membrane
      1. Glucose
      2. Water
      3. Carbon Dioxide
    2. Large molecules must be broken down first
      1. Starch
2. Transport into and out of cells
  1. Diffusion
    1. Passive transport
      1. Does not require energy
    2. Movement of molecules from a region of high concentration to an area of lower concentration
      1. Down a concentration gradient
    3. Diffusion continues to occur until the molecules are evenly spread (there is no longer a concentration gradient)
    4. Diffusion is essential to maintain life. Cells need to be able to take in food and oxygen and remove waste materials
  2. Concentration Gradient
    1. Difference in concentration between two solutions, cells or solutions and cells
  3. Osmosis
    1. The diffusion of water
    2. Movement of WATER molecules from a region of high WATER concentration to a region of lower WATER concentration
      1. Down a concentration gradient
    3. Hypertonic
      1. Smaller water concentration
    4. Isotonic
      1. Equal water concentration
    5. Hypotonic
      1. Greater water concentration
  4. Active Transport
    1. Movement of molecules from a region of low concentration to a region of higher concentration
      1. Against a concentration gradient
    2. Requires energy
    3. Proteins in the cell membrane act as pumps to carry the molecules/ions into the cell
    4. Potassium and sodium ions move through the membranes of nerve cells by active transport
  5. Animal Cells and Water
    1. Higher water concentration(Hypotonic)
      1. Water passes into the cell by osmosis from high water concentration to lower water concentration
        Cell swells and bursts
    2. Equal water concentration(Isotonic)
      1. No net loss of gain of water
        Cell remains unchanged
    3. Lower water concentration(Hypertonic)
      1. Water passes out of the cell by osmosis from high water concentration to lower water concentration
        Cell shrinks
  6. Plant Cells and Water
    1. High water concentration(Hypotonic)
      1. Water passes into the cell by osmosis from high water concentration to lower water concentration
        Vacuole increases in size and cell membrane is pushed against the cell wall
        The cell is TURGID
    2. Equal water concentration(Isotonic)
      1. No net loss or gain of water
        Cell remains unchanged
    3. Low water concentration(Hypertonic)
      1. Water passes out of the cell by osmosis from high water concentration to lower water concentration
        Vacuole shrinks and cell membrane pulls away from the cell wall
        Cell is PLASMOLYSED
Producing New Cells
1. Chromosomes
  1. The nucleus of most body cells contain two matching sets of chromosomes
    1. The cell is said to be diploid if it has two matching sets of chromosomes in its nucleus
  2. Chromosome Complement
    1. Number and type of chromosomes that a cell contains
  3. Each chromosome contains genes, which are composed od DNA (Deoxyribonucleic Acid)
2. Mitosis and Cell Division
  1. Mitosis is controlled by the nucleus of the cell
  2. Importance of Mitosis
    1. Increases the number of cells
      1. Required for growth and repair
    2. Ensures that no genetic information is lost
  3. Process of Mitosis
    1. Diploid parent cell. The individual chromosomes coil up and become visible
    2. Each chromosome replicates so that an exact copy of the DNA is made. The chromosomes now consist of two chromatids joined by a centromere
    3. The chromosomes line up at the equator of the cell. Spindle fibres attach to each chromatid.
    4. The spindle fibres shorten, pulling the chromatids apart, towards opposite poles of the cell.
    5. The nuclear membranes reform and the cytoplasm divides.
    6. There are now two daughter cells that are identical to each other and the original parent cell.
3. Cell Culture
  1. Cells can undergo mitosis in an artificial environment
    1. This is called cell culture
  2. Importance of cell culture in society
    1. Yeasts can be cultured for the baking and brewing industries
    2. Bacteria can be cultured for the dairy industry
    3. Skin cells can be cultured for skin grafts
  3. Aseptic Techniques
    1. Prevent the growth of other cells, e.g. bacteria
    2. Prevent contamination
    3. Examples
      1. Long hair tied back
      2. Protective clothing (lab coat, gloves, safety glasses) worn
      3. Wash hands before and after working with cultures
      4. Use a cell culture hood
      5. Ensure there are no open windows/draughts
      6. Sterilise all equipment
      7. Perform experiments as quickly as possible to minimise contamination risk
  4. Requirements for cell production by cell culture
    1. Appropriate growth medium
      1. Nutrient agar or broth
    2. Availability of oxygen
    3. Suitable pH
    4. Suitable temperature
DNA and the Production of Proteins
1. Structure of DNA
  1. The nucleus of living cells contains genetic information organised into chromosomes.
  2. Chromosomes are made up of regions called genes.
  3. Genes are made up of DNA (Deoxyribonucleic Acid)
  4. DNA carries the genetic information, which is required for the production of proteins.
  5. A DNA molecule is described as a double stranded helix
    1. Each strand of DNA carries bases, of which, there are four
      1. Adenine (A)
      2. Thymine (T)
      3. Guanine (G)
      4. Cytosine (C)
      5. The strands are held together by bonds between the bases on each strand
        The bases bond together to make complementary base pairs
        Adenine always pairs with Thymine
        Guanine always pairs with Cytosine
        The complementary base pairings can be remembered by the fact that the letters A and T are both made up of straight lines only and G and C both have a curve in them.
2. Genetic Code
  1. The genetic code is determined by the sequence of the bases A, T, G and C
  2. The base sequence of a specific gene determines the sequence of amino acids
    1. The sequence of amino acids determines what protein will be produced
    2. There are 20 amino acids that occur naturally
3. Protein Synthesis
  1. Proteins are assembled from amino acids at the ribosomes, found in the cytoplasm
  2. The DNA in the nucleus is too large to pass through the nuclear membrane, so mRNA (Messenger RNA) carries a copy of the code from the DNA
    1. The mRNA travels through the nuclear membrane, to a ribosome, where the amino acids are joined together in the correct order
      1. The amino acids form a long chain and eventually, a protein is formed
Proteins and Enzymes
1. The variety of proteins comes from the fact that there are many ways which the 20 amino acids can be arranged
2. The shape of a protein molecule affects its function
3. Protein Functions
  1. Antibodies
    1. Involved in defence
      1. Fight disease/ infection
  2. Hormones
    1. Chemical messengers
    2. Travel in the bloodstream
  3. Receptors
    1. Receive external signals
    2. Provide a binding site for molecules
  4. Structural
    1. Provide strength and support to cellular structures
  5. Enzymes
    1. Act as biological catalysts
4. Enzymes
  1. Enzymes are biological catalysts
    1. A catalyst speeds up a reaction
    2. Enzymes are biological catalysts since they speed up reactions that occur inside cells
      1. Without enzymes, essential life
  2. Remain unchanged by the process of speeding up a reaction
    1. They can be used over and over again
  3. Enzymes are specific
    1. They can only catalyse (speed up) one reaction
  4. Active Site
    1. The region of the enzyme which the substrate binds to
      1. Substrate
        The substance that the particular enzyme works on
    2. Shape of the active site is complementary to the shape of the substrate
      1. This makes an enzyme specific
        Only one type of molecule can fit into the active site, so an enzyme can only catalyse one reaction
  5. Substances produced by enzyme action
    1. Products
  6. Types of reaction
    1. Synthesis
      1. Two (or more) substances being combined to make one product
    2. Degradation
      1. Breaking up the substrate into two (or more) products
  7. Optimum
    1. Each enzyme works best under its optimum conditions
      1. When the conditions are optimum, the enzyme is at its most active and the reaction cannot happen any faster
    2. The optimum is different for different enzymes
    3. Temperature
      1. Warmer conditions
        Enzyme and substrate molecules move around faster
        Therefore, they meet more regularly
        Rate of reaction increases
      2. High temperatures
        Shape of the active site changes
        Substrate and active site are no longer complementary
        Enzyme no longer works
        The enzyme is described as being DENATURED
      3. For many human enzymes, the optimum temperature is 35-40 degrees Celsius
        Body temperature is 37 degrees Celsius (approx.)
    4. pH
      1. pH also affects enzyme activity
        At extremes in pH, the active site can change shape and the enzyme no longer works
      2. The optimum pH of an enzyme varies depending on its function in the body
Genetic Engineering
1. Genetic information can be transferred between cells naturally or artificially
  1. Natural methods
    1. Fertilisation in animals/ plants
    2. Transfer of plasmids between bacterial species
    3. Viruses
  2. Artificial method
    1. Genetic engineering
2. Stages in genetic engineering
  1. 1. Identify the section of chromosome that contains the required gene
    1. 2. Extract the required gene
      1. Plasmid removed from bacterial cell and cut open
        3. Insert the required gene into the plasmid
        4. Insert the plasmid into a host cell
        5. Cell is cultured and the required product is isolated and harvested
3. Not always, but often includes the use of bacteria
4. Pieces of chromosome are transferred form the donor to the recipient
5. Genetic engineering is carried out by humans to allow a species to make a protein that is normally made by another species
6. There are many benefits and issues associated with GM organisms
7. Following genetic engineering, the transformed cells are cultured to produce a GM (Genetically Modified) strain or organism
8. Vector
  1. A vector is a method of transferring genetic material from a donor to a recipient
    1. Examples
      1. Plasmids
      2. Viruses
      3. Bacterial cells
Photosynthesis
1. The method by which green plants make carbohydrate (food)
2. Photosynthesis is a series of enzyme controlled reactions
3. Two Stage Process
  1. Stage 2
    1. Carbon fixation stage
      1. Hydrogen, from the light dependent stage is combined with carbon dioxide to produce sugar
        Energy from ATP allows this to happen
  2. Stage 1
    1. Light dependent stage
      1. Light energy from the sun is trapped by chloroplasts
        Light energy is converted into chemical energy in the form of ATP
        ATP= Adenosine Triphosphate
      2. Water is split into hydrogen and oxygen
        Excess oxygen diffuses out of cell
4. Raw materials
  1. Carbon dioxide
  2. Water
5. Products
  1. Glucose
  2. Oxygen
6. Limiting Factors
  1. A limiting factor is a variable that, when in short supply, can limit the rate of photosynthesis
  2. The rate of photosynthesis is limited by
    1. Temperature
    2. Light Intensity
    3. Carbon Dioxide Concentration
7. Uses of sugar produced in photosynthesis
  1. To release energy in respiration
  2. Converted into starch or cellulose
    1. Starch acts as a store of energy in plants
    2. Cellulose is the main chemical component of plant cell walls
Respiration
1. Aerobic Respiration
  1. Glucose is completely broken down
  2. Requires Oxygen
  3. Glucose + Oxygen → Carbon Dioxide + Water + Energy (38 ATP)
  4. 1. Glucose is broken down into pyruvate, forming 2 ATP molecules
    1. 2. The pyruvate is broken down into carbon dioxide and water, producing 36 ATP molecules
      1. Occurs in the mitochondria, oxygen required
    2. Occurs in the cytoplasm, no oxygen required
2. Anaerobic Respiration
  1. In animals cells
    1. Glucose → Lactic Acid + Energy (2 ATP)
    2. 1. Glucose is broken down into pyruvate, forming 2 ATP molecules
      1. Occurs in the cytoplasm, no oxygen required
      2. 2. Pyruvate is converted into lactic acid
        When oxygen becomes available, the lactic acid is converted back into pyruvate and the second stage of aerobic respiration occurs as normal
  2. In plant and yeast cells
    1. 1. Glucose is broken down into pyruvate, forming 2 ATP molecules
      1. 2. Pyruvate is broken down into ethanol and carbon dioxide
        The reaction cannot be reversed as the carbon dioxide produced is released
      2. Occurs in the cytoplasm, no oxygen required
    2. Glucose → Ethanol + Carbon Dioxide + Energy (2 ATP)
  3. Occurs in the absence of oxygen
  4. Glucose is not completely broken down
  5. Also called fermentation
3. Respiration is the chemical release of energy from food through a series of enzyme controlled reactions
4. The release and use of energy
  1. The energy released from the respiration of glucose is used to form ATP from ADP (Adenosine Diphosphate) and Phosphate
    1. ATP is a high energy molecule
  2. The chemical energy stored in ATP can be released by breaking it back down into ADP and phosphate
  3. The energy generated through respiration can be used for cell activities
    1. Muscle cell contraction
    2. Cell division
    3. Protein synthesis
    4. Transmission of nerve impulses

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National 5 Biology: Cell Biology

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