Protein synthsis

Question 1

Where does protein synthesis occur in cells?

Answer 1

• On the ribosomes.

Question 2

What are the two stages for production of protein from the DNA code? Give NAMES.

Answer 2

• Transcription.
• Translation

Question 3

What is “transcription?”

Answer 3

• Transcription is where one gene on DNA is copied into complementary mRNA (in the nucleus.)

Question 4

What is “translation ?”

Answer 4

• Translation = production of polypeptides from the sequence of codons carried by mRNA ie, mRNA attached to ribosome/ corresponding tRNA molecules bring the specific amino acid the codon codes for.

Question 5

Why is it useful than mRNA is a lot shorter than DNA?

Answer 5

• This means that the mRNA is able to carry the genetic code to the ribosome to enable the protein to be made.

Question 6

What are the 5 main steps of transcription?

Answer 6

1.) DNA helix unwinds (hydrogen bonds between bases broken by DNA helicase) to expose the bases to act as template.
2.) Only one strand acts as a template.
3.) Free mRNA nucleotides (in nucleus) are attracted to their complementary base pairs on template DNA strand.
4.) RNA polymerase joins together adjacent RNA nucleotides (by phosphodiester bonds) to create RNA polymer chain. One entire gene is copied.
5.) Once copied, pre- mRNA is spliced and then leaves nucleus through nuclear pores.

Question 7

What particular structures/ molecules are involved in translation?

Answer 7

• Ribosomes
• tRNA
• ATP (in order to form peptide bonds between amino acids in polypeptide chain.)
• mRNA

Question 8

In eukaryotes, what does transcription lead to the production of?

Answer 8

• Results in production of pre-mRNA.
• Introns in the pre-mRNA are spliced out to form mRNA; mRNA then leaves nucleus/ takes part in translation.

Question 9

In prokaryotes, what does transcription result directly in? Ie. what step do prokaryotes miss - compared to eukaryotes?

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Answer 9

• Results directly in production of mRNA from DNA (there is no pre-mRNA!!)
• Prokaryotes miss out splicing step - as their genes don’t contain introns.

Question 10

What is the role of the ribosome in translation?

Answer 10

• The ribosome will hold the mRNA/ tRNA in place, allowing the anticodon and the codon to allign.

Question 11

What are the steps of translation?

6 main steps

Answer 11

1.) Modified mRNA (that left nucleus) will attach to a ribosome.
2.) The ribosomes attaches at the start codon (on the mRNA.)
3.) tRNA has complementary anticodon to the start codon/ will allign opposite the mRNA - held in place by ribosome.
4.) Ribosome moves along mRNA to enable another complementary tRNA to attach to the next codon on mRNA.
5.) Amino acids delivered by tRNA are joined by peptide bond (catalysed by enzyme/ requires ATP.)
6.) Continues until ribosome reaches STOP codon at end of mRNA. Stop codon doesn’t code for amino acid/ ribosome detaches from polypeptide chain / translation ends.

Question 12

What do we need in order to form peptide bonds between the amino acids that the tRNA has delivered to the mRNA?

Answer 12

• ATP
• Enzyme (acting as catalyst.)

Question 13

What happens after the polypeptide chain is complete ie. translation has stopped?

Answer 13

• The polypeptide chain created will enter Golgi appartus for folding and modification.