DNA

• DNA


  deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes and is the carrier of genetic information.
• coded information


  all the instructions to put an organism together that make it work
• what do inherited characteristics depend on?

  what's in your DNA
• where is DNA found?

  nucleus of cells in long structures called chromosomes
• chromosomes


  threadlike structures made of DNA molecules that contain the genes
• chromosomes normally come in...

  pairs
• DNA is a...


  polymer that is made up of two strands coiled together in the shape of a double helix
• gene


  a segment of DNA found on the chromosome that codes for a particular sequence of amino acids, which are put together to make a specific protein and thus determines a trait
• how many amino acids are used?

  20, but they make up thousands of different proteins
• what do genes tell us?

  what order to put amino acids in
• what does DNA determine?

  what proteins the cell produces (e.g. haemoglobin, keratin, etc.), which determines what type of cell it is (e.g. red blood cell, skin cell, etc.)
• genome


  the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes
• human genome


  complete sequence of genes in the human body
• why is understanding the human genome important for science and medicine?

  - allows scientists to identify genes in the genome that are linked to different types of disease

  - knowing which genes are link to inherited diseases could help us understand them better and could help us develop effective treatments for them

  - the human genome is mostly identical in all individuals, but tiny differences have been developed as people migrated from the common ancestor and studying these differences can help scientists work out when new populations split off
• DNA is made up of...

  nucleotides
• nucleotides


  the monomer of DNA - basic units of DNA molecule, composed of a phosphate, a sugar and one of 4 DNA bases
• DNA bases


  A, T, C, G
• complementary base pairing

  where each base of a nucleotide links to a base on the opposite strand in the helix

  - in DNA, T pairs with A; G pairs with C;

  - in RNA, U pairs with A and G pairs with C
• what do the order of bases in a gene decide?

  the order of amino acids in a protein
• what is each amino acid coded for by?

  a sequence of three bases in a gene called a triplet
• amino acids are...


  joined together to make various proteins, depending on the order of the gene's bases
• non-coding parts of DNA

  there are parts of DNA that don't code for proteins - some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed (used to make a protein)
• RNA


  a single-stranded nucleic acid that passes along genetic messages
• where are proteins made?

  ribosomes in the cytoplasm
• what do ribosomes do to make proteins?

  use the code in the DNA found in the nucleus, however it cannot move out of it due to its large size, so mRNA is used to get the code from the DNA to the ribosome
• mRNA


  messenger RNA; type of RNA that copies and carries instructions from DNA in the nucleus to the ribosome - the correct amino acids are brought to the ribosomes in the correct order by carrier molecules
• when an amino acid has been assembled...

  it folds into a unique shape, which allows the protein to perform the task its ment to do
• protein functions


  - enzymes: act as biological catalysts

  - hormones: used to carry messages around the body

  - structural proteins: strengthen bodily structures
• mutations


  a random error in gene replication that leads to a change in an organism's DNA - they can sometimes be inherited
• mutation occurrence


  they occur continuously and can occur spontaneously (e.g. when a chromosome isn't quite replicated properly)
• effects of mutations on proteins

  most have very little to no effect on the protein, some will change it to such a small extent that its function or appearance is unaffected and some mutations can seriously affect a protein, where it could change its shape and affect its ability to perform its function
• what can alter how genes are expressed?

  a mutation in a non-coding DNA
• insertion


  where a new base in inserted into the DNA base sequence where it shouldn't be and this changes the way the DNA base sequence is read, which can change the amino acids they code for. insertions can change more than one amino acids acid as they have a knock-on effect on the bases further on in the sequence
• deletion


  when a random base is deleted from the DNA base sequence, changing the way the base sequence is read and has knock-on effects further down the sequence
• substitutions


  when a random base in the DNA base sequence is changed to a different base
• what do mutations change?

  the sequence of bases in DNA - changes in bases can affect the amino acids sequence, and therefore the protein coded for