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Learning Goal - Protein Synthesis

16 important questions on Learning Goal - Protein Synthesis

List the roles of RNA ploymerases in the process of transcription.

Roles of RNA polymerase basically encompass everything done by helicase and DNA polymerase 3: it can bind to the DNA site that needs to be transcripted, unwind the DNA double-helix to expose the indivdiual template strand, initiate transcription by adding RNA nucelotides to form the pre-mRNA strand, and detach from the template strand, allowing the seperated DNA strands to re-wind.
Key: Unwinding, Initiation, Role of DNA Polymerase 3, Termination, Detaching

State the complementary base pairing utilised in transcription.

Adenine paired with uracil instead of thymine, guanine paired with cytosine.

Distinguish between the sense and antisense strands in DNA.

The antisense strand is the DNA template strand that undergoes transcription, it's base sequence is naturally complementary to that of the pre-mRNA synthesised. The sense strand is the opposite strand not used in this process, and has the same base sequence as the mRNA synthesised, except, wherever there is thymine in the sense strand, there is uracil in the pre-mRNA.

Outline how the stability of the DNA is mantained.

Basically, the individual DNA strands that come about after unwinding the double-helix structure are extremely vulnerable to the chemical environment surrounding it, and there is the risk of DNA degradation/mutation that can change the base sequence of the original DNA strand, which absolutely cannot happen, given how it will affect the individual when its base sequences are replicated and transcribed in the future. Hence, the transcription of the antisense strand only happens for a short time to prevent this occurrence, in order to reduce the time where the individual strands are vulnerable to chemical changes.

State the location where polypeptides are synthesised.

Cytoplasm.

State the complementary base pairing utilized in translation.

The complementary base pairing between tRNA and mRNA follows the rule that adenine must be paired with uracil and guanine must be paired with cytosine. All three codon bases must be complementary to all 3 anticodon bases.

Explain the reason that a sequence containing 3 nucleotides are required to code for 20 amino acids commonly utilized by all organisms.

3 nucleotides per codon sequence allows 64 possible combinations in total. Although only 20 amino acids (+ 4 more combinations for the start and stop codons) are required, 64 combinations allows for the degeneracy of the genetic code, reducing the chance of possible mutations having harmful effects.

State the cause of sickle cell anemia, including the differences in HbA and HbS alleles.

A point mutation that changes the sixth codon of the gene that codes for the haemoglobin protein from GTG to GUG, causing the sixth amino acid attached in the polypeptide sequence to be valine instead of glutamine, turning that part of the protein from hydrophobic to hydrophilic, hence changing the shape/folding of the protein. HbA refers to the normal haemoglobin allele containing glutamine whereas HbS refers to the affected one.

Discuss symptoms of sickle cell disease.

Slower clotting of blood (due to anemia), pain crises (due to vessel blockage), fatigue (due to low SA:V ratio of cells that reduce gas exchange efficiency of blood cells --> an individual essentially uses up the same amount of oxygen in a faster amount of time)

Outline the structure and functions of the promoter region in DNA.

The promoter region in the DNA is located just before the coding region of a particular gene (the transcription unit), and is composed of a 100 to a 100 nucleotides. Its binding with RNA polymerase leads to the transcription of the gene. The structure/sequence of promoter regions can be similar for a set of genes that can belong to different chromosomes, leading all genes to be expressed at the same time.

Define "coding" and "non-coding" sequences of DNA.

Coding: DNA sequences that can code for, and eventually to synthesise a polypeptide, and hence, a protein.

Non-coding: DNA sequences that do not code for, and hence, lead to synthesis of a protein.

Outline the benefits of alternative RNA splicing.

This process allows multiple proteins to be produced from the same mRNA strand, and hence the same gene. Hence, proteome (number of proteins DNA can produce) is larger than the genome itself, allowing for the efficiency of protein production as a gene does not need to be duplicated again and again and again for every single gene.

List types of modifications of polypeptides that may be required to form a functional protein.

Modifications of the polypeptide involving folding, cleavage, and general transformation into secondary, tertiary and quaternary protein occurs in the RER, while chemical modification involving the addition of fats/carbohydrates etc. Occur in the Golgi body (for formation of glycoproteins etc.).

Outline the stages of modification of preproinsulin to form function insulin.

Preproinsulin comes in the form of a 110-nucleotide long chain. It is converted to mature insulin by:
1) removal of signal peptide, whose purpose was to guide the molecule into the lumen of the RER, to convert the molecule into proinsulin,
2) moving from RER to Golgi body, where proinsulin folds and 2 disulphide bonds are formed between the A-chain and B-chain of the molecule, to stabilise it,
3) and removal of the C-chain, leaving the final form of insulin to be just the A-chain, B-chain, and the 2 disulphide bonds connecting them.

List reasons for why proteins typically exist for a relatively short time within a cell.

1) Cell's activity could change e.g. Cell could move from one stage of the cell cycle to the next, where certain proteins may not be needed anymore.
2) Protein could be exposed to reactive elements such as free radicals that cause alteration of the shape, resulting in loss of function.
3) Protein could be misfolded or denatured in other ways, and hence, unusable.

Outline the function of proteasomes in the recycling of amino acids.

Proteins who have lost the use of their function, and are no longer usable are tagged by a short chain of proteins known as ubiquitin, which act as a signal to proteasomes that these proteins should be digested. The proteasomes subsequently break down these proteins into shorter chains of peptides known as oligopeptides. The enzymes in the cytoplasm further break down these oligopeptides into fully usable amino acids, that are used again in protein synthesis.

The question on the page originate from the summary of the following study material:

Biology HL

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