UNIT 4 (topic 2) protein synthesis

Question 1

what are the stages of protein synthesis

Answer 1

1) transcription
2) splicing
3) translation

Question 2

explain the stage of transcription

Answer 2

• process of making pre-mRNA
• DNA helicase breaks the H bonds and unwinds the strands of DNA
• free RNA nucleotides bond to complementory bases (A-U and C-G) on the template strand
• RNA polymerase creates phosphodiester bonds and forms the pre-mRNA
• pre-mRNA breaks away from the template strand and the two DNA strands bond back together

Question 3

what is a codon

Answer 3

the sequence of 3 bases on mRNA that codes for a single amino acid

Question 4

what is the difference with introns and exons

Answer 4

exons - coding
introns - non-coding

Question 5

explain splicing

Answer 5

• specific enzymes cleave pre-mRNA at specific points to remove introns
• exons join back to form mature mRNA

Question 6

what is alternative splicing

Answer 6

if a DNA sequence has many exons, they can be arranged in multiple ways to make different polypeptides

Question 7

explain the steps of translation

Answer 7

• first two codons of mRNA attach to the ribosome
• tRNA wiht a complementory anticodon pairs with the first codon, forming a H bond, carrying an amino acid along with it
• another tRNA with a complementory anticodon pairs with the second codon, forming a H bond, carrying the second amino acid
• peptide bond formed between the two amino acid with the help of a catalysed enzyme and ATP - beginning of the polypeptide chain
• ribosome moves the mRNA along to bind to the third codon
• the first tRNA detaches and leaves the amino acids

Question 8

describe the structure of mRNA

Answer 8

ribose sugar, single-stranded, nitrogenous bases of A-U and C-G, can vary with size depending on cell size and type

Question 9

describe the structure of tRNA

Answer 9

ribose sugar, clover leaf shape with a few H bonds, A-U and C-G, varies with size depending on cell size and type