Biology Pack 5 - DNA, ATP, Mitosis

Nucleic acids
1. gene is a section of DNA that holds the code for making polypeptides
2. Nucleotide structure
  1. Bases in DNA:
    1. Adenine, Thymine, Guanine, Cytosine
  2. Bases in RNA:
    1. Adenine, Guanine, Cytosine, uracil
  3. The three components are joined up by a condensation reaction
  4. Nucleotides joining up
    1. Two mononucleotides can join to form a di-nucleotide by a condensation reaction
      1. between the OH group on carbon number 3 and the phosphate group attached to C5 of another
      2. Lots of them = polynucleotide
    2. The bond formed between nucleotides is a phosphodiester bond
3. DNA
  1. DNA used to be considered to have too few components
    1. DNA consists of four chemically similar nucleotides whereas proteins consist of twenty amino acids which are more chemically diverse
  2. Watson and Crick, Wilkins and Franklin
    1. Watson and Crick worked out the structure of DNA in 1953
      1. Their findings were based on the work of Wilkins and Franklin
        They used X-ray diffraction techniques to study the structure of DNA
  3. Structure of DNA
    1. The sugar in DNA (the pentose) is called deoxyribose
    2. DNA is doubled stranded
      1. Made up of two polynucleotide strands
    3. The sugar and phosphate group are on the outside of the molecule and the bases in the centre
      1. Or a sugar-phosphate "backbone"
    4. Adenine pairs with Thymine with 2 hydrogen bonds
      1. Cytosine pairs with Guanine with 3 hydrogen bonds
    5. The two strands run in opposite directions to each other
      1. Anti-parallel
  4. Relating structure of DNA to its function
    1. DNA has a sugar phosphate backbone
      1. This gives it stability and strength protecting the bases on the inside
    2. DNA is a very stable molecule
      1. It can be passed on accurately from one generation to the next
    3. DNA is a very large molecule
      1. It can hold a lot of information
    4. DNA is a coiled molecule
      1. This makes it compact
    5. DNA has a sequence of nitrogen bases
      1. Allows information to be stored
    6. DNA is double stranded
      1. Replication can occur semi-conservatively
    7. DNA has complimentary base pairing
      1. Ensures accurate replication
    8. The hydrogen bonds between the base pairs are weak
      1. Enables strand separation for replication
    9. There are many hydrogen bonds between base pairs
      1. Makes the molecule strong/stable
DNA replication
1. Replication is Semi conservative
  1. Each new molecule of DNA has one strand from the original molecule and one new strand
  2. 1. The enzyme DNA helicase unwinds the double helix, hydrogen bonds between pairs are broken
    1. 2. Each unzipped strand now acts as a template and free nucleotides are attracted to exposed bases
      1. Base pairing takes place with hydrogen bonds between complimentary bases
        A-T G-C
      2. 3. The enzyme DNA polymerase joins the nucleotides together along the sugar-phosphate backbone
        Two identical new DNA molecules are formed
2. Meselsohn and Stahl's experiment
  1. This found out whether replication was conservative or semi conservative
  2. They used bacteria with two different isotopes of nitrogen, 14N and 15N (15N being heavier)
    1. The DNA containing 15N would be heavier than the DNA containing 14N
      1. Bacteria would take up the nitrogen and it would be put into their DNA
        Firstly a control of 14N was used to show it was light
        2. Bacteria was grown in 15N, it sunk lower in the test tube than 14N
        The remaining bacteria were transferred to a medium with only 14N
        The 1st generation where 14N only replicated once, there was one strand 14N and one strand 15N so it floated halfway in test tube
        2nd generation there were now 2 generations, one generation floated to the top and the other stayed in the middle
Ribonucleic acid (RNA)
1. This is a single polynucleotide which is shorter than DNA
2. The sugar in RNA is ribose
3. Four bases are:
  1. Uracil, Adenine, Guanine, Cytosine
4. 3 main types of RNA
  1. Messenger RNA
    1. Transfers information from DNA to ribosomes
  2. Ribosomal RNA
    1. Associated with proteins, rRNA makes ribosomes
  3. Transfer RNA
    1. Carries specific amino acids to the ribosomes during protein synthesis
ATP
1. Structure
  1. ATP is a nucleotide derivative and is made up of three parts
    1. Adenine (nitrogen containing base)
    2. Ribose (pentose sugar
    3. A chain of 3 phosphate groups
2. Release of energy from ATP
  1. The bonds between three phosphate groups in ATP are unstable and have a low activation energy
  2. When a bond is broken energy is released
    1. ATP + H2O --> ADP + Pi +E
      1. The enzyme that catalyses this is ATP hydrolase
      2. It is a hydrolysis reaction
3. Synthesis of ATP
  1. ADP + Pi + E --> ATP + H2O
    1. ATP synthase catalyses this reaction
    2. This is a condensation reaction
  2. ATP is synthesised in cells during reactions that release energy such as:
    1. During photosynthesis in chlorophyll containing plant cells in photophosporylation
      1. during respiration in animals and plant cells in oxidative phosphorylation
        In plant cells and animal cells when phosphate molecules are transferred from donor molecules to ADP in substrate-level phosphorylation
      2. (Using energy from light to make ATP)
4. Roles of ATP
  1. Because of the instability of its phosphate bonds ATP cannot be stored
    1. So it provides an immediate energy source for the cell
  2. Used in:
    1. Metabollic processes
    2. Movement (muscle contraction)
    3. Active transport
    4. Secretion
    5. Activation of molecules
5. Phosphorylate = adding phosphate
Cell division
1. The cell cycle
  1. 1. Interphase
    1. G1
      1. Organelles replicate, proteins also formed
    2. S
      1. DNA replication occurs each chromosone now made up of chromatids
    3. G2
      1. Continued organelle replication
  2. 2. Mitosis (PMAT)
    1. Prophase
      1. Chromosones become visible
      2. Chromosones shorten and thicken
      3. Centrioles move to opposite poles
      4. Spindle fibres develop
      5. Nucleolus and nuclear envelope disapear/break down
    2. Metaphase
      1. Chromosones clearly seen to be made of 2 sister chromatids
      2. Spindle fibres attach to centromeres
      3. Chromosones line up along equator of cell
    3. Anaphase
      1. Centromeres divide, spindle fibres contract
      2. Chromatids move to opposite poles of cell
    4. Telophase
      1. Chromosones reach poles
      2. Chromosones become longer and thinner and disapear
      3. Spindle fibre disintegrates
      4. Nuclear membranes and nucleoli reform
    5. Mitotic index
      1. This is the ratio of cells undergoing mitosis to those cells in interphase
    6. Cancer
      1. Genes that promote cell division = proto-oncogenes
        Genes that limit it are tumour suppressor genes
        If these don't work then cells mutate randomely
      2. Malignant spreads to surrounding cells and can break off and travel round the blood
      3. Benign grows slowly and is less life threatening
  3. 3. Cytokensis
    1. Equal distribution of organelles and cytoplasm into daughter cells
2. Chromosones
  1. Chromosones carry the genes that control protein synthesis
    1. These determine characteristics
  2. Homologous chromosones are diploid (ie they have pairs)
    1. Humans have 23 chromosones but 46 is the diploid number
    2. Haploid = half homologous chromosones
  3. Allele = different version of the same gene
3. Prokaryotes
  1. 1.Circular DNA replicates, both copies attach to cell membrane, plasmids replicate
    1. 2. Cell membranes grow between 2 DNA molecules dividing cytoplasm into 2
      1. 3. New cell wall forms
        4. Two daughter cells result with single copy of DNA and variable number of plasmids
4. Viruses
  1. They attach to host cells and inject their genetic material
    1. The infected host cell produces all components of virus and are then assembled into new viral particles

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Biology Pack 5 - DNA, ATP, Mitosis

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	Created by Jacob Shepherd over 8 years ago