Practice Exam Essay Question - Protein Synthesis PDF

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BIOL10008 Tutorial practice exam essay question Q2 Describe the processes of protein production in a cell from i. ii. iii. iv.

the transcription of a gene for a protein the translation into protein transport through the endomembrane system the export of that protein from the cell

10 marks, 10 mins. Marking scheme i.

The gene is a segment of DNA in the nucleus coding for a sequence of amino acids (1 mark)

DNA is unwound so that with the right promotors in place one strand is transcribed by RNA polymerase into RNA (1 mark) Some processing will happen to the RNA transcript before it leaves the nucleus as mRNA (1 mark)

ii.

mRNA leaves the nucleus and travels to the rough ER (1 mark)

Ribosomes attached to the rough ER facilitate translation of the mRNA transcript to form a polypeptide (a chain of amino acids) (1 mark) One codon (sequence of 3 nucleotides in the mRNA) codes for one amino acid) tRNA binds with a complementary anti-codon (1 mark) The amino acids are joined in a chain and the polypeptide is formed within the lumen of the ER. (1 mark)

iii.

The polypeptide travels through the ER, where the 2°, 3° and 4° structures form (2 mark) 2° structure = folding into alpha helices or beta sheets 3° structure = 3-dimensional folding, often due to disulphide bonds between cysteine residues in the polypeptide 4° structure = multiple polypeptides come together to form a single protein

Most proteins are then packaged into vesicles and travel from the ER to the Golgi apparatus (1 mark)

iv.

In the Golgi, carbohydrate chains may be added to proteins (1 mark)

Proteins may be modified, then sorted and packaged into labeled vesicles (1 mark) Vesicles enter the Golgi at the cis face and leave the Golgi from the trans face (1 mark) Vesicles travel from the Golgi to the cell membrane where exocytosis occurs or may travel within the cell to other organelles (1 mark)

For this question, the marking scheme adds up to more than 10! This is sometimes the case – you don’t need to cover ALL the points in the marking scheme to gain full marks. Sometimes, the marking scheme includes marks for good expression and a logically structured answer. Try to avoid a random list of bits of information....