t17 inheritance

• The nucleus contains chromosomes 
• Chromosomes:

  Thread-like structures of DNA which carry genetic information in the form of genes
• DNA (stands for deoxyribonucleic acid) is the chemical that all of our genetic material is made of
• DNA is a polymer (made up of lots of similar units stuck together)
• DNA has 2 strands which are stuck together to form a double helix (double stranded spiral)
• to make sure DNA is compact enough to fit in the nucleus it is separated into 46 different sections. these sections are tight coils which form a chromosomes
• Each of our cells have 46 chromosomes which is the same as 23 pairs of equal chromosomes, except the 23rd chromosomes as these are the sex chromosomes (X chromosome and Y chromosome)
• Women have 2 X chromosomes 

  Men have 1 X and 1 Y chromosome
• Gene:

  Small section of DNA that codes for a protein (‘small segment of a chromosome’)
• A gene is a code for a sequence of animo acids
• In a particular sequence the amino acids form a protein
• There are only 20 different types of amino acids and 1000’s of different proteins
• DNA determines which  proteins the cell produces which determines what type of cell it is (e.g. red blood cells need a lot of the protein haemoglobin)
• Genome:

  Entire set of genetic material in an organism
• As now we know the complete human genome we can now identify genes that are linked to certain types of diseases
• Inherited diseases are genes inherited from parents that cause disease or increase the risk.
• The X chromosome (recessive) looks like a big s and the Y chromosome (dominant) is a little stick.
• Protein synthesis:

  The process of making proteins
• Transcription:

  Taking a single gene of DNA and copying it into a structure called mRNA
• translation:

  Taking mRNA and using it to produce a protein
• DNA have genes which have a specific sequence of bases that are able  to code for a specific sequence of amino acids which when combined form a particular protein
• In order to make a protein the specific sequence of bases has to be read by a ribosome which are outside of the nucleus.

  Since the DNA is so big it can’t leave the nucleus. We need to make a copy of the single gene (so tis small enough to leave the nucleus) which is called mRNA (messenger RNA)
• mRNA:

  Copy of a single gene
• mRNA is much shorter than DNA, is only a single strand, instead of containing the base thymine it contains uracil.
• In transcription the enzyme RNA polymerase which binds to the DNA just before where the gene we want to copy starts (TEMPLATE STRAND), then just ahead of the enzyme the 2 strands of DNA separate making all their bases exposed. The enzyme moves along the DNA strand and read the bases one by one and use them to make an mRNA strand.
• mRNA bases will always be complementary to DNA bases ( meaning C & G always pair on an mRNA, G & C pair, T & A , A & U (on mRNA) &, A & T (DNA)).
• a + t and c + g in dna 


  a + u and c+ g in mrna
• Once the enzyme is finished making the mRNA strand the enzyme detaches from the DNA and the DNA strand can close back up
• The mRNA then leaves the nucleus and heads to the ribosome
• Template strand:

  The section of the DNA that is used to make the mRNA
• Triplet/codon :

  A group of 3 bases
• Each triplet codes for a specific amino acid
• mRNA strand and the ribosome both bind together 

  The ribosome makes the protein by adding one amino acid at a time

  The amino acids are Brough to the ribosome by tRNA (transfer RNA) which have the amino acid at the top (like a jelly fish with a dot) and the anti-codon  (sequence of 3 bases which are complimentary to the 3 bases at the beginning of the mRNA which code for the amino acid the tRNA is carrying) at the bottom
• As the ribosome moves along the mRNA the tRNA bonds to the complementary codon on the mRNA allowing the first tRNA to detach leaving the amino acid behind bonding with the rest completing a chain of amino acids. The amino acid chain detaches from the ribosome and folds up on itself to form a protein.
• Mitosis 

  First stage: the DNA replicates to form 2 copies of each chromosome (46 chromosomes)

  Second stage: one set of chromosomes is pulled to each end of the cell , the nucleus also divides

  Third stage: the cytoplasm and the cell membrane divide to form 2 identical cells
• Meiosis is the process where 2 gametes (haploid cells) combine to form a normal cell (diploid cell)
• In the 1st division of meiosis:

  • First stage: replicate all of the cell's DNA by replicating all of the chromosomes (making them pairs)
  • Second stage: chromosomes line up in the center of the nucleus randomly
  • Third stage: chromosome pairs are pulled apart and the whole cell splits into 2 randomly distributed cells