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DNA: The code of Life, ...................................................…

- - - - During prophase of the cell cycle, the chromatin becomes more condensed & takes the form of chromosomes
      - Chromosomes are sausage-shaped structures, rather than the loose network of chromatin
      - Chromosomes become visible during mitosis & meiosis during prophase
      - Biologists cut out images of the chromosomes & arrange them in order of size, to form a karyotype
      - The human karyotype shows we have 46 chromosomes that occur in 23 pairs
      - There are 22 pairs of autosomes & 1 pair of sex chromosomes (gonosomes) that can be XX (female) or XY (male)
      - Karyotypes help diagnose genetic disorders
    - - A gene is a small portion of DNA with a specific sequence that determines a particular characteristic of an organism
      - Genes determine what an organism looks like and how it behaves
      - Genes are the functional units that pass the characteristics down through generations
      - Organisms don't inherit whole characteristics as unit; they inherit individual genes
      - Genes work by coding for protein molecules, which carry out functions in the cell & outside the cell
      - Not all DNA forms genes; Only 1% of DNA codes for proteins
    - - Located in these organelles in the cytoplasm of the cell:
        
        Mitochondria in animal & plant cells called Mitochondrial DNA
        
        Chloroplasts in plant cells
    - - Isolating nucleic acids is the 1st step to be taken when studying DNA & RNA
      - The basic method can be used for extracting both DNA & RNA
      - There is much more DNA than RNA in cells
      - Start by collecting the sample from which to extract DNA
      - You need to get the maximum DNA yield from the sample
    - - DNA is tightly wound around proteins to form a dense network of fibres called chromatin
      - DNA is packaged to protect it & to control which parts are active at a given time
      - If you unwound the DNA of a single minute cell, it would be over 2m long
    - - The rest 99% are called non-coding DNA or nonsense DNA
      - Some of these DNA regulates gene copying by responding to signals from the cell & turning gene copying 'on' or 'off'
  - - - DNA is made up of a large number of repeated units called Nucleotides
      - Each is composed of 3 different organic molecules:
      - There are 4 different nitrogenous bases:
        
        Guanine(G)
        
        Smaller molecules called Pyrimidines:
        
        Thymine(T)
        
        Cytosine(C)
        
        Adenine(A)
    - - DNA molecule consists of nucleotides joined together in long chains
      - Chemical bonds form between the sugar group of 1 nucleotide & the phosphate group of the next nucleotide
      - A DNA strand is a polymer
      - In double-stranded DNA, there are 2 sugar-phosphate chains running in opposite directions, & complementary nitrogenous bases form hydrogen bonds between them
      - Double-stranded DNA creates the appearance of a ladder
    - - How DNA was discovered to be a double helix
        
        Read paragraph on page 21
        
        Scientific Method
      - The sugar & phosphate molecules are water soluble, while the bases are hydrophobic
      - The bases stack themselves in centre of DNA spiral to avoid water
      - The bases form a twisted ladder, keeping the sugar & phosphates on the outside
  - - - Genes contain the genetic instructions needed to make other components of cells
      - Like the proteins & RNA molecules used in the development & functioning of all known living organisms & some viruses
    - - Large sections of DNA don't code for genes but maintain the structure of the chromosome & regulate the function of genes that contain the coded genetic info
      - These sections are non-coding or nonsense DNA
    - - Proteins, which are coded by DNA, are both structural & functional
      - Proteins are important components of all cells & molecules like enzymes & hormones etc.
    - - DNA contains the hereditary info that is passed on from parents to offspring
      - Natural selection takes place to ensure useful genetic changes are passed on to next generation
    - - The ability of DNA to replicate itself during mitosis means cells can divide into new cells with an exact copy of the DNA
  - - - Starts when the cell forms & Ends when it divides into 2 daughter cells
      - Cell cycle has 2 parts:
        
        Second is Mitosis - which is cell Division
        
        Mitosis
        
        The chromosomes separate into 2 sets.
        
        (Cytokinesis): The cytoplasm forms 2 daughter cells that now enter the G1 phase of growth - (Restart cycle)
        
        First is Interphase - which is cell Growth
        
        1st gap phase (G1)
        
        A cell performs its normal metabolic functions & grows until its appropriate surface area to volume ratio (SVA) is reached
        
        Synthesis phase (S)
        
        The DNA content of the nucleus duplicates into 2 parts
        
        2nd gap phase (G2)
        
        The cell produces microtubules to separate the chromosomes during mitosis
      - Typical human cell has 46 chromosomes
      - When cell divides by mitosis, 2 daughter cells are formed, each with 46 chromosomes.
        
        Meaning the new chromosomes have been formed to produce 2 sets of identical DNA
    - - DNA replicates in Prokaryotic & Eukaryotic cells
      - A single double-stranded DNA molecule will form 2 identical DNA molecules
    - - When human cell divides & its DNA replicates, it has to copy the exact sequence of 3 billion nucleotides
        
        To ensure daughter cells will inherit correct characteristics & functions
      - There can be copying errors in which the wrong nucleotide or too many or too few nucleotides are inserted into a sequence
      - Most replication mistakes are corrected through DNA repair process by repair enzymes
        
        Some errors make it past the repair processes and become permanent mutations
        
        Some mutations are of no consequence
        
        Some can lead to genetic problems or cancer
        
        Some are useful & help organisms survive
        
        Some are natural & important to allow species to adapt
    - - DNA replication in biotechnology & genetic engineering is important for:
        
        Cloning cells in tissue culture
        
        Gene splicing to produce resistance to certain diseases & to manufacture antibiotics, insulin, growth hormone & genetically modified organisms
        
        DNA profiling & forensics
        
        Paternity & maternity testing
        
        Genetic counselling of parents to inform them about inheritable disorders & conditions
    - - In cell division to produce new cells & tissues
      - To maintain chromosome number & ensure that the same genes are in every cell
      - To help with growth through protein synthesis
      - To regenerate damaged or ageing tissues through mitosis
      - For production of spores & vegetative growth in asexual reproduction
      - To produce gametes through meiosis in sexual reproduction
      - For creating new cells for growth, repair & replacement of worn or damaged cells
  - - - 1 Sample DNA is extracted & put in test tube
      - 2 The DNA is cut into fragments using a restriction enzyme. This is an enzyme that recognizes specific DNA sequences & cuts the DNA at that point
      - 3 DNA fragments of different sizes are produced, depending on how far apart the sequences are
        
        Electrophoresis is used to show differences in size
        
        In this technique an electric current runs DNA through a gel
        
        Tiny space in gel let smaller fragments move faster through it
        
        The pieces of DNA are separated by size
      - 4 The DNA is mixed with a fluorescent substance to show up the bands under ultraviolet light
      - 5 The band pattern can be compared with known DNA sample.
    - - DNA profiling is controversial
        
        Arguments for it are:
        
        It can be used to solve crimes
        
        It can determine paternity
        
        It can help people find missing relatives
        
        It can identify people
        
        Arguments against it are:
        
        It invades the privacy of the victim & suspect
        
        Tests can be tampered with
        
        The technology can be misused
- - - - Adenine(A)
      - Cytosine(C)
      - Guanine(G)
      - Uracil (U)
  - - - This is copied from sections of DNA in nucleus & is used in cytoplasm to manufacture protein
    - - This is produced from DNA in the nucleus & is used in cytoplasm to manufacture protein
    - - Made of proteins & rRNA
      - The nucleolus, in nucleus of eukaryotic cells, is the site of ribosome manufacture
      - Ribosomes are essential for protein synthesis
      - Ribosomes are found free in cytoplasm or attached to tubules of rough endoplasmic reticulum
  - - - Meaning the gene carries the instructions for the formation of RNA from RNA nucleotides
    - - Sequence determines the type of protein
  - - - Translation
        
        Happens in cytoplasm
        
        RNA translated into proteins by structures attached to rough endoplasmic reticulum, called ribosomes
        
        In cytoplasm tRNA are anticodons
        
        tRNA collect free-floating amino acids in cytoplasm
        
        tRNA moves to ribosome where mRNA strands have attached
        
        anticodons on tRNA match the bases on codons of mRNA
        
        Amino acids carried by tRNA become attached by peptide bonds to form required protein
        
        Each tRNA is released to pick up more amino acids
        
        Process is controlled by enzymes
      - Transcription
        
        Happens in nucleus
        
        mRNA strands are transcribed from DNA by enzyme named RNA polymerase
        
        New mRNA sequences are complementary to their DNA template, not identical copies
        
        Transcription happens in nucleus as follows:
        
        DNA strands unwind & unzip
        
        Hydrogen bonds break
        
        One strand is used as template to form mRNA using free nucleotides from nucleoplasm
        
        The coded message for protein synthesis is copied as the mRNA
        
        mRNA moves out of nucleus through a nucleopore
        
        mRNA carries triplet code from DNA also called Codon
        
        mRNA attaches itself to ribosome
    - - mRNA strand attaches itself to any ribosomes in cell
      - A tRNA molecule transfers amino acid to ribosome in sequence determined by mRNA codons
      - mRNA codon carries code for specific amino acid
      - An anticodon is sequence of 3 bases found on tRNA
      - Each new amino acid links with previous by forming peptide bond
      - Amino acids chain lengthens into polypeptide in process called elongation
      - After polypeptide chain is synthesised, the protein is formed
      - Physical structure of proteins determines how they interact with other molecules