L13: Revision & prokaryotic protein synthesis

Question 1

Sequence of AA in protein

Answer 1

Held together by covalent bonds (peptide bonds)

Read from amino terminus to carboxyl terminus

Unique characteristic of every protein

Encoded by nucleotide sequence of DNA

Question 2

Side groups

Answer 2

Affect protein structure and function

Example: hydrophobicity. Tryptophan and glutamine

Question 3

Protein structure

Answer 3

Secondary structure: folding; alpha helix

Tertiary structure: packing; polypeptide chain

Quaternary structure: interaction; assembled subunits

Question 4

Example of when primary sequence affect protein function

Answer 4

In normal Hb: has Glu -> not hydrophobic

In sickle Hb: has Val -> hydrophobic, no polarity -> change in structure of Hb -> sickle shape

Question 5

Translation

Answer 5

Occurs in cytoplasm

Complex process- requires >300 molecules in eukaryotes

mRNA- used as template to guide synthesis of chain of AA -> protein

Protein synthesis occurs at ribosomes. Ribosomes composed of RNAs (rRNA) & proteins

tRNA delivers AA to synthesise polypeptide chain

Question 6

Polycistronic mRNA

Answer 6

Carry several open reading frames . Each of which can be translated into polypeptide

Question 7

Eukaryotic mRNA

Answer 7

Monocistronic

Contains genetic info to translate single protein chain (polypeptide)

Question 8

Ribosomes

Answer 8

Protein biosynthesis occurs by process of translation on ribosomes

Prokaryote: ribonucleoprotein particles found in cytosol of all cells. 20,000 ribosomes in cell, 20% of cell’s mass. 70S ribosome (2 subunits: 50S, 30S). Composed of RNA and protein.

Question 9

Eukaryote translation

Answer 9

Electron micrograph of polysomes

Multiple ribosomes translating same mRNA

Ribosomes move toward 3’ end of mRNA

Proteins synthesised N-terminal to C-terminal