protein synthesis

Question 1

where is DNA contained in a cell

Answer 1

• within a double membrane called the nuclear envelope which encloses the nucleus.
• this protects the DNA from being damaged in the cytoplasm

Question 2

what is transcription

Answer 2

• the process of copying the base sequence of genes to transport them to the ribosome
• this produces shorter molecules called RNA

Question 3

How is DNA unzipped for transcription

Answer 3

• DNA helicase unzips the double helix by breaking the hydrogen bonds between bases
• helicase only unzips the section of DNA that contains the gene, beginning at a start codon

Question 4

which strand contains the code for a protein

Answer 4

• The sense strand runs from 5’ to 3’
• The antisense strand runs from 3’ to 5’ and is the complementary copy of the sense strand, and does not code for a protein.
• The antisense strand acts as a template strand so that the complementary RNA formed carries the same base sequence as the sense strand

Question 5

what does the enzyme RNA polymerase do

Answer 5

• phosphodister bonds are formed between RNA nucleotides
• these were free nucleotides which base pair with complementary bases exposed on the antisense strand

Question 6

when does transcription stop and what happens after

Answer 6

• at the end of the gene
• the completed short strand of RNA is called mRNA (messanger)
• the mRNA detaches from the DNA and the DNA double helix reforms
• the mRNA molecule leaves nucleus via nuclear pore and travels to the ribosome in the cytoplasm

Question 7

what are ribosomes made up of

Answer 7

• 1 small subunit and 1 large subunit
• these subunits are composed of almost equal amounts of protein and rRNA
• rRNA maintains structural ability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction

Question 8

what is translation

Answer 8

• mRNA binds to specific site on the small subunit of a ribosome
• ribosome holds mRNA in position when it is translated into a sequence of amino acids

Question 9

what is tRNA

Answer 9

• transfer RNA
• necessary for translation of mRNA
• composed of RNA folded in such a way that 3 bases (anticodon) are at 1 end of the molecule
• this anticodon will bind to the complementary codon on mRNA
• tRNA molecules carry the amino acid corresponding to the complementary codon

Question 10

how are the amino acids brought together in the correct sequence to form the protein

Answer 10

• tRNA anticodons bind to complementary codons along the mRNA
• amino acids are added one at a time
• amino acids are brought together in the correct sequence for the primary structure of the protein coded for by the mRNA
• peptide bonds are formed between amino acids in condensation reactions
• this is catalysed by enzyme peptidyl transferase