D1.2 Protein Synthesis

Give four examples of proteins and a one word description of its role

1. Collagen - structural

2. Hemeglobin - transports oxygen in RBCS

3. Insulin - signals blood to be taken into cells in the blood

4. Trypsin - digestive enzymes for breaking down protein macromolecules

Describe the roles of RNA polymerase in RNA synthesis

• Unwinds DNA double helix

• Break cbp hydrogen bonds of bases

• Build sugar-phosphate backbones of the mRNA strand using cbp of the mRNA strand and DNA strand

Describe gene expression and factors that could affect it.

• Refers to how much genetic information is used to produce functional products like proteins through activity of transcription, translation, etc.

• transcription is highl controlled beause it is the first step of gene expression.

• Factors: type of cell, external esignals, time, age.

Explain steps of DNA transcription with a labeled diagram

Transcription factors bind on to the promoter of the DNA sequence, guiding the initiation of transcription. RNA polymerase binds to the promoter and then separates the double-stranded DNA of the coding sequence (by breaking the hydrogen bonds between base pairs). Free RNA nucleotides then align opposite their complementary base pair and RNA polymerase joins them together with covalent bonds (between the sugar-phosphate backbone) from the 3’ end of the previous one with the 5’ end of the new one . Whe the terminator sequence is reached the synthesised RNA transcript is released and the DNA double helix reforms.

What is the effect of DNA transcription on the DNA

None. there is no effect on it and it stays stable.

What is DNA translation? (location, required molecules & organelles, product)

• takes place in the cytoplasm

• requires mRNA, tRNA, ribosomes, amino acids (AA)

• produces a polypeptide chain

Draw a labeled diagram of a chain of polypeptide

monomers of amino acids, joined by peptide bonds, forming a chain of polypeptide/ protein

Different combinations of AA bonded makes various structures

3 types of RNA and there function

mRNA (messenger): contains the code for building the protein

tRNA (transfer): brings the amino acid that corresponds to the mRNA codon, to the ribosome

rRNA (ribosomal)

Explain steps of DNA translation using a labeled diagram

A small subunit of ribosome binds to mRNA and slides from the 5’ end to the start codon (usually AUG into the amino acid Met). The initiator tRNA (usually UAC) binds to the start codon, then the large subunit binds to that tRNA via the P site, completing the ribosomal complex. Another tRNA molecule with a complementary anitcodon to the codon enters at the A site and forms a peptide bond between the two AAs at the A and P site. The ribosome translocates along one codon position (in a 5’ → 3’ direction), tRNA in P site now holds the polypeptide chain. The deacylated tRNA is now in the E site and is released. A new tRNA molecule enters the unoccupied A site and the process of amino acid elongation is repeated. This cycle continues the length of the codon sequence until a stop codon is reached. A release factor binds at the A site and causes both the ribosome and the polypeptide chain to dissociate from the mRNA – completing the process of translation.

Definition for mRNA codon and tRNA anticodon

mRNA codon: 3 nucleotide sequence that corresponds to a tRNA and an AA

tRNA anticodon: 3 nulceotide sequence that base pairs with an mRNA codon

triplets ensure reliability of the process, making no wrong amino acids

Draw a diagram of a ribosome’s strucutre

Small subunit: binds to the mRNA molecule

Large subunit: location of the poplypeptide chain and tRNA entrance and exit. Has space for 3 tRNAs but only really has 2 at a time.

• make of ribosomal RNA (rRNA) and other proteins

How many possible codons and amino acids are there?

64 codons

20 amino acids

• Many codons can code for the same amino acid —> degenracy

• The same codons, code for the same amino acids in every organism on Earth with very few exceptions, evidence for LUCA