Topic 7.3 Flashcards
1
Q
Initiation stage in translation
A
- the small ribosomal subunit binds to the 5’ end of the mRNA strand & slides along in a 5’-3’ direction until it reaches the start codon on the mRNA strand (AUG)
- the appropriate tRNA molecule bind to the codon on the mRNA strand via its anticodon(UAC) (according to complementary base pairing)
- the large ribosomal subunit aligns itself to the tRNA molecule at the P site and forms a complex with the small subunit
2
Q
What does initiation involve?
A
The 1st stage of translation involves the assembly of the three components that carry out the process (mRNA, tRNA, ribosome)
3
Q
What are the stages of transcription
A
- initiation
- elongation
- translocation
- termination
4
Q
Elongation
A
- the anticodon of incoming tRNA pairs w its complementary mRNA codon at the amino acid site(A site) of the ribosome
- the amino acid at the P site is covalently attached to the amino acid at the A site via a peptide bond (condensation reaction)
- the tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site carries the peptide chain
5
Q
Translocation
A
- The ribosome moves along the mRNA strand by one codon position (in a 5’→ 3’direction)
- The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site
- Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
6
Q
Termination
A
- involves the disassembly of the components and the release of a polypeptide chain
- Elongation and translocation continue in a repeating cycle until the ribosome reaches a stop codon
- These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals for translation to stop
- The polypeptide is released and the ribosome disassembles back into its two independent subunits
7
Q
Primary protein structure
A
- theorder / sequence of amino acids which comprise the polypeptide chain
- formed bycovalent peptide bondsbetween the amine and carboxyl groups ofadjacent amino acids
- controls all subsequent levels of protein organisation because it determines the nature of the interactions between R groups of different amino acids
8
Q
Secondary protein structure
A
- the way a polypeptide folds in arepeating arrangement to formα-helices andβ-pleated sheets
- folding is a result ofhydrogen bondingbetween the amine & carboxyl groups ofnon-adjacentamino acids
- Sequences that do not form either an alpha helix or beta-pleated sheet will exist as a random coil
- Secondary structure provides the polypeptide chain with a level of mechanical stability (due to the presence of hydrogen bonds)
9
Q
Tertiary protein structure
A
- the way the polypeptide chain coils and turns to form a complex molecular shape (i.e. the3D shape)
- caused byinteractions between R groups; including H-bonds, disulfide bridges, ionic bonds and hydrophobic interactions
- Relative amino acid positions are important (e.g. non-polar amino acids usually avoid exposure to aqueous solutions)
- Tertiary structure may be important for the function of the protein (e.g. specificity of active site in enzymes)
10
Q
Quaternary protein structures
A
- Multiple polypeptidesor prosthetic groupsmay interact to form a single, larger, biologically active protein (quaternary structure)
- prosthetic group → an inorganic compound involved in protein structure or function (e.g. the heme group in haemoglobin)
- A protein containing a prosthetic group is called a conjugated protein
- Quaternary structures may be held together by a variety of bonds (similar to tertiary structure)
11
Q
What is a polysome?
A
a group of two or more ribosomes translating an mRNA sequence simultaneously
12
Q
How are differences in polypeptide length affected by the polysome cluster?
A
Ribosomes located at the 3’-end of the polysome cluster will have longer polypeptide chains than those at the 5’-end
13
Q
What is protein destination determined by?
A
by the presence or absence of an initial signal sequence on a nascent polypeptide chain
