Unit 1 Topic 3

Question 1

What is the first stage of gene expression?

Answer 1

Transcription

Question 2

What is the second stage of gene expression?

Answer 2

Translation

Question 3

What makes up an RNA nucleotide?

Answer 3

a ribose sugar
a base (Uracil instead of Thymine)
a phosphate

Question 4

Is RNA double or single stranded?

Answer 4

single stranded

Question 5

What are the three main types of RNA involved in protein synthesis?

Answer 5

•mRNA
•tRNA
•rRNA

Question 6

Give details of mRNA

Answer 6

for the synthesis of a protein, the particular sequence of bases on the DNA is first transcribed into the complementary sequence of mRNA. this message RNA can then carry the information for a protein through the nuclear envelope to the sites of protein synthesis (the ribosomes). Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid

Question 7

Give details of tRNA

Answer 7

This type of RNA is responsible for the transport and transfer of individual amino acids during protein synthesis. Amino acids are transported by specific tRNA molecules, which recognise the genetic code presented by the mRNA. The three bases exposed at the bottom form the anticodon. This is the complementary base sequence to the base sequence on mRNA coding for a particular amino acid

Question 8

Give details of rRNA

Answer 8

This type of RNA is bound to structural proteins to form a ribosome. The ribosome is used in the synthesis of proteins

Question 9

Describe the events that take place during transcription

Answer 9

Transcription is the first step in protein synthesis. Information from DNA is copied into an RNA molecule, a process which takes place in the nucleus. The RNA polymerase enzyme moves along the DNA, unwinding the double helix and breaking the hydrogen bonds that hold the base pairs together. Free RNA nucleotides bond with the complementary base pairs on the DNA. The base pairing rules are summarised in the table below. The RNA nucleotides are held in place by hydrogen bonds while strong bonds form between the phosphate of one nucleotide and the ribose sugar of the adjacent nucleotide. When transcription is complete, the RNA polymerase enzyme and the mRNA strand that has been constructed are released. The mRNA that has been produced at this stage is known as the primary transcript.

Question 10

What happens after a eukaryotic cell transcribes a protein coding gene

Answer 10

RNA splicing

Question 11

Where does RNA splicing happen?

Answer 11

in the nucleus

Question 12

What is the product of RNA splicing?

Answer 12

mature mRNA transcript

Question 13

What happens during RNA splicing?

Answer 13

The introns of the primary transcript are non-coding regions and are removed. The exons are coding regions and are joined together to form the mature mRNA transcript

Question 14

What is true about the order of the exons?

Answer 14

The order of the exons is unchanged during splicing

Question 15

What happens after transcription?

Answer 15

translation

Question 16

Where does translation take place

Answer 16

on ribosomes in the cytoplasm

Question 17

What other type apart from mRNA is required for translation?

Answer 17

tRNA

Question 18

Provide information about tRNA

Answer 18

The amino acid is linked to the amino acid attachment site of the tRNA molecule
tRNA- a single RNA strand that folds back on itself to form a three-dimensional structure with an amino acid binding site at one end. A loop of nucleotides protruding from the other end includes the specialised anticodon sequence
Anticodon- a specialised base triplet that binds to a specific mRNA codon

Question 19

What name is given to the three bases exposed at the base of the tRNA molecule?

Answer 19

anticodon

Question 20

What name is given to each group of three bars on mRNA?

Answer 20

codon

Question 21

What happens during translation?

Answer 21

As an mRNA molecule passes through a ribosome, each codon is translated into an amino acid. The tRNA molecule carrying the complementary anticodon binds briefly to the mRNA codon. The amino acid attached to the tRNA is then added to the polypeptide chain being synthesised. Amino acids are joined together by strong peptide bonds. After the amino acid has been added to a polypeptide chain during translation, the tRNA is free to pick up another amino acid in the cytoplasm

Question 22

What type of bond holds amino acids together in a polypeptide?

Answer 22

peptide bonds

Question 23

What happens to the polypeptide chain once it is completed?

Answer 23

It is released from the ribosome. Further processing, such as folding and binding to other polypeptide chains, results in the formation of a mature protein. The mRNA molecule is usually reused to produce more identical polypeptide chains

Question 24

What three codons do not code for amino acids?

Answer 24

UGA, UAA and UAG

Question 25

What are UGA, UAA and UAG all known as?

Answer 25

Stop codons

Question 26

what do stop codons do?

Answer 26

single where translation ends

Question 27

What codon is usually the start codon in eukaryotes?

Answer 27

AUG

Question 28

Why can many proteins be made from just one gene?

Answer 28

The mRNA can be edited in different ways by assembling different sequences of exons for translation. As a result many different mature transcripts of mRNA can be derived from one section of DNA

Question 29

What is the process in which many mature transcripts of mRNA can be made from one gene called?

Answer 29

alternative RNA splicing

Question 30

What is the result of alternative RNA splicing?

Answer 30

different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained

Question 31

what determines a proteins function?

Answer 31

it’s shape

Question 32

what bonds hold the shape of a polypeptide

Answer 32

hydrogen

Question 33

what is phenotype determined by

Answer 33

the proteins produced as a result of gene expression

Question 34

what can also influence phenotype

Answer 34

environmental factors