AS Level Oxford AQA Biology Chapter 8 - Protein synthesis

genetic code

the ordering of nucleotides in DNA molecules that carries the genetic information in living cells

Triple codon system

Every 3 bases codes for 1 amino acid.

The genetic code is:

universal, degenerate (more than 1 code for each amino acid), non-overlapping.

Polypeptide

A polymer (chain) of many amino acids linked together by peptide bonds.

mRNA

messenger RNA; type of RNA that carries instructions from DNA in the nucleus to the ribosome

pre-mRNA

precursor mRNA; the first strand of mRNA produced by gene transcription that contains both introns and exons

Transcription

(genetics) the organic process whereby the DNA sequence in a gene is copied into mRNA

Splicing

removal of introns

Exons

Coding segments of eukaryotic DNA.

Introns

Noncoding segments of nucleic acid that lie between coding sequences (exons).

DNA helicase

An enzyme that unwinds the DNA double helix during DNA replication

RNA ploymerase

enzyme that links together the growing chain of RNA nucleotides during transcription using a DNA strand as a template

Transcription process

1. A large transcription complex made of RNA polymerase and other proteins recognizes the start of a gene and begins to unwind the segments of DNA

2. RNA polymerase uses one strand of the DNA as a template. RNA nucleotides form complementary base pairs with the DNA template. G pairs with C and A pairs with U. the growing RNA strand hands freely as it is transcribed. Then the DNA strand closes back together

3. A completed RNA stand separates from the DNA template and the transcription complex falls apart

translation

Process by which mRNA is decoded and a protein is produced

tRNA

transfer RNA; type of RNA that carries amino acids to the ribosome

Ribosomes

site of protein synthesis

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon

peptide bond

The chemical bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid

Translation process

1. the exposed codon in the first site attract complementary tRNA bearing an amino acid. The tRNA pairs with the mRNA codon, bringing it very close to the other tRNA molecule

2. the ribosome forms a bond between the two amino acids and breaks the bond between the first tRNA and its amino acid

3. the ribosome pulls the mRNA strand the length of one codon. The first tRNA is shifted into the exit site, where it leaves the ribosome and returns to the cytoplasm to recharge. The first site is again empty by exposing the next mRNA codon.

protein folding

The physical process by which a polypeptide folds into its characteristic three-dimensional structure, which is essential to the protein's function.

chaperone proteins

help other proteins fold correctly

primary structure

sequence of amino acids

secondary structure

The second level of protein structure; the regular local patterns of coils or folds of a polypeptide chain.

teritary structure

The complex 3-dimensional structure of a single peptide chain; held in place by disulfide bonds between cysteines.

quaternary structure

The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits.

Incorrect Folding of Proteins

Can occur from hydrophobic groups on the amino acids join together.