Unit 1 - Gene Expression Key Area 3

Question 1

What is meant by the term gene expression

Answer 1

Gene expression is the process where information in a gene is used to produce a functional gene product, usually a protein.
Gene expression involves the transcription and translation of DNA sequences.

Question 2

How is gene expression controlled

Answer 2

Gene expression is controlled by the regulation of Transcription and Translation

Question 3

Are all genes expressed within a cell

Answer 3

Only a fraction of genes in a cell are expressed

Question 4

What determines the sequence of amino acids

Answer 4

The order of bases on DNA determines the sequence of amino acids that are made

Question 5

What do amino acids join together to make

Answer 5

The sequence of amino acids joined together in polypeptide chain determines the structure, shape and function of the protein produced.

Question 6

What is RNA and what is it made up of

Answer 6

RNA is another type of nucleic acid
RNA nucleotides contain a ribose sugar, a phosphate and a base
RNA is single stranded

Question 7

State the complementary bases found in RNA

Answer 7

Adenine - Uracil

Cytosine - Guanine

Question 8

What is the role of mRNA

Answer 8

Messenger RNA (mRNA) carries a copy of the DNA code from the nucleus to the ribosome.

Question 9

What is the role of rRNA

Answer 9

ribosomal RNA - along with proteins forms a ribosome

Question 10

What is the role of tRNA

Answer 10

transfer RNA - carries a specific amino acid to the ribosome.

Question 11

What are the two processes involved in expressing a gene

Answer 11

There are two processes to express a gene:
- Transcription
coping the code from the original DNA
- Translation
converting the code into an amino acid sequence and therefore a protein

Question 12

Where does Transcription occur

Answer 12

Transcription occurs in the nucleus

Question 13

Describe the steps of transcription

Answer 13

• copying the code
  Stages in Transcription
  1) RNA polymerase enzyme moves to the specific section of DNA and unwinds and unzips the DNA double helix by breaking hydrogen bonds between the bases
  2) RNA polymerase adds nucleotides by complementary base pairing forming a primary transcript of mRNA

Question 14

What is RNA splicing and why is it important

Answer 14

RNA splicing is a process that removes non coding regions from the primary transcript
It is important because NOT ALL nucleotides in a gene play a role in the coding for the amino acids sequence

Question 15

What is the difference between introns and exons

Answer 15

The primary transcript produced is made up of exons (coding) and introns (non-coding) regions

Question 16

What is removed from the primary transcript and what is formed as a result

Answer 16

The INTRONS must be REMOVED from the primary mRNA transcript.
This process forms the mature mRNA transcript.

Question 17

Where does the mature transcript travel to

Answer 17

The mature transcript travels to the cytoplasm. The order of exons remains unchanged.

Question 18

What is translation

Answer 18

Translation is the synthesis of a protein from the mature mRNA transcript produced in transcription

Question 19

What is a mRNA codon

Answer 19

Each triplet of bases on the mRNA molecule is called a CODON and codes for a specific amino acid.

Question 20

Describe the structure of tRNA

Answer 20

• These amino acids are carried by tRNA
• tRNA folds due to complementary base pairing
• Each triplet of bases on a tRNA is called an anticodon
• The codon and the anticodon pair together by complementary base pairing
• A tRNA molecule has an anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end.

Question 21

Where does mRNA travel to in the cytoplasm

Answer 21

mRNA travels to a ribosome in the cytoplasm

Question 22

Describe the structure and function of a ribosome

Answer 22

• Ribosomes are small spherical structures made up of ribosomal RNA and protein
• A ribosome’s function is to bring tRNA into contact with mRNA
• They have binding sites for both tRNA and mRNA

Question 23

Steps of Translation (1-4)

Answer 23

1) Translation begins with a start codon on the mRNA
2) The ribosome binds with the mRNA to ensure the start codon is in place
3) Each tRNA picks up specific amino acids in the cytoplasm and carries it to the ribosome
4) The anticodon of a tRNA carrying the correct amino acid binds to a complementary codon on the mRNA lining up the amino acids in a specific order.

Question 24

Steps of Translation (5-8)

Answer 24

5) Peptide bonds form between the amino acids to form a growing polypeptide chain
6) A stop codon is present at the end of the mRNA
7) When the chain is complete it detaches from the ribosome
8) When the tRNA detaches from its amino acid, it then collects another

Question 25

Explain how different proteins can be expressed from one gene

Answer 25

• During RNA splicing, depending on circumstances, alternative segments of RNA may be treated as exons and introns
• The same primary transcript can produce several different mature transcripts depending on where it is spliced
• This is called alternative RNA splicing
• This means that different proteins can be expressed from one gene

Question 26

Explain how the three dimensional shapes of proteins form

Answer 26

• Amino acids are linked by peptide bonds to form polypeptides.
• Polypeptide chains fold to form the three-dimensional shape of a protein,
• held together by hydrogen bonds and other interactions between individual amino acids.
• Proteins have a large variety of shapes which determines their functions.

Question 27

What is meant by phenotype and what can influence them

Answer 27

Phenotype is the visible characteristics of an organism which occur as a result of its genes and the proteins expressed.
Environmental factors can influence phenotype e.g. availability of nutrients

Question 28

What RNA’s are involved in Transcription and Translation

Answer 28

Transcription and translation involves three

types of RNA (mRNA, tRNA and rRNA).

Question 29

a) What is mRNA transcribed from

b) What is mRNA translated to

Answer 29

a) mRNA is transcribed from DNA in the nucleus and b) translated into proteins by ribosomes in the cytoplasm.

Question 30

What does RNA Splicing form?

Answer 30

RNA splicing forms a mature mRNA

transcript.

Question 31

What is formed when exons are joined together?

Answer 31

The exons are coding regions and are joined

together to form the mature transcript.