KA : 1.3 Gene Expression

Question 1

What is gene expression?

Answer 1

Gene expression is the process by which specific genes are activated to produce a required protein. It involves the transcription and translation of DNA sequences. Only a fraction of genes in a cell are expressed.

Question 2

What is RNA?

Answer 2

RNA (Ribonucleic acid) plays a vital role in the production of protein from the code in DNA.

Question 3

What are RNA’s 4 bases?

Answer 3

Adenine, Uracil, Cytosine and Guanine

A → U
C → G

Question 4

What are the differences between DNA and RNA?

Answer 4

DNA is double

Question 4

What are the differences between DNA and RNA?

Answer 4

DNA is double stranded, is composed of deoxyribose sugar and has bases A, T, C and G.
RNA is single stranded, is composed of ribose sugar and has bases A, U, C and G.

Question 5

What are the 3 types of RNA that are involved in transcription and translation?

Answer 5

1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)

Question 6

What is the role of mRNA?

Answer 6

mRNA is formed (transcribed) in the nucleus from free nucleotides and carries a copy of the DNA code from the nucleus to the ribosome (where protein synthesis occurs).
Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid.

Question 7

What is the role of tRNA?

Answer 7

tRNA molecules collect amino acids and bring them to the ribosome to build proetins, each tRNA molecule carries its specific amino acid to the ribosome. A tRNA molevules has an anticodon (exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other.

Question 8

What is an anticodon?

Answer 8

An anticodon is an exposed triplet of bases.

Question 9

What is the role of rRNA?

Answer 9

rRNA molecules combine with proteins to create the ribosome - which is responsible for assembling proteins following the DNA code.

Question 10

What is a codon?

Answer 10

Each triplet on a mRNA molecule is called a codon and codes for a specific amino acid.

Question 11

What is transcription?

Answer 11

The synthesis of mRNA from a section of DNA.
Transcription of a gene starts from a region of DNA known as the promoter and ends at the terminator.

Question 12

What do the concepts promoter and terminator mean?

Answer 12

Promoter is the start of a gene.
Terminator is the end of a gene.

Question 13

“RNA _______ binds at the promoter and _____ the DNA. This breaks the _________ bonds between the base pairs.”

Answer 13

RNA polymerase binds at the promoter and unwinds the DNA. This breaks the hydrogen bonds between base pairs.

Question 14

Stages within RNA polymerase and transcription

Answer 14

1. Unwinds the DNA whilst breaking the hydrogen bonds.
2. Then adds nucleotides onto the ‘3 end of the growing mRNA molecule.
3. The molecule gets longer until it reaches the terminator.

This molecule is called the primary transcript.

Question 15

What are introns and exons?

Answer 15

Introns are non-coding regions.
Exons are coding regions.

Question 16

Stages of RNA splicing

Answer 16

1. After the mRNA has been transcribed the introns are removed.
2. The remaining exons are spliced together to form a continuous sequences called the mature transcript.
3. The mature transcript then leaves the nucleus to travel to the cytoplasm and attach to a ribosome.
   The order in which the exons lie is unchanged during splicing.

Question 17

What is the mature and primary transcript?

Answer 17

Mature transcript is a continuous sequence.
Primary transcript is stopped by a terminator so is a non-continuous process.

Question 18

What is a start codon and its function?

Answer 18

A start codon is the first codon of a mRNA transcript translated by a ribosome.

Question 19

What is a stop codon and its function?

Answer 19

Stop codons signal the end of the polypeptide chain during translation. They are also known as nonsense codons or termination codons as they don’t code for amino acids. UAG, UAA and UGG are stop codons.

Question 20

How do codons and anticodons bond?

Answer 20

Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids.

Question 21

“Peptide bonds form between adjacent ____/____ to form a _____ (protein)”

Answer 21

Peptide bonds form between adjacent amino acids to form a polypeptide (protein).

Question 22

What is the structure of a ribosome and its function?

Answer 22

Ribosomes are small, roughly spherical structures found in all cells.
The ribosomes function is to bring the tRNA molecules bearing amino acids in contact with the mRNA.

Question 23

Stages of translation

Answer 23

1. Ribosome binds to 5’ end of mRNA template so that the mRNA’s start codon (AUG) is in position.
2. tRNA picks appropriate amino acid (methionine - start codon) from the cytoplasm.
3. The tRNA carries amino acid to ribosome and becomes attached by hydrogen bonds between anticodon (UAC) and start codon (AUG).
4. tRNA now enters the ribosome and the amino acid on this tRNA bonds to growing polypeptide chain.
5. Process repeated lots to translate mRNA into complete polypeptide chain.
6. When a stop codon is reached the ribosome releases polypeptide. Whole process requires energy from ATP.