Chapter 6- Transcription and translation (1)

Question 1

What are histones?

Answer 1

Histones are proteins that coil and structure the DNA of eukaryotic cell nuclei into units called nucleosomes.

Question 2

What does the histone octamer consist of?

Answer 2

Consists of 2 copies of each histone protein.

Question 3

How many times does DNA coil around the octamer to form the nucleosome?

Answer 3

Twice

Question 4

What does a nucleotide consist of?

Answer 4

It consists of a nitrogen containing base connected to a 5-carbon sugar (Pentose sugar) and a phosphate group.

Question 5

What can the sugar be in a nucleotide?

Answer 5

1- Ribose = RNA

2- Deoxyribose = DNA

Question 6

What part of the nucleotide is the structural element?

Answer 6

The sugar and phosphate of a nucleotide

Question 7

What are the four possible nitrogenous bases available in DNA?

Answer 7

1- Adenine (A)
2- Thymine (T)
3-Cytosine (C)
4- Guanine (G)

Question 8

What are the four possible nitrogenous bases available in RNA?

Answer 8

1- Adenine (A)
2- Uracil (U)
3-Cytosine (C)
4- Guanine (G)

Question 9

Bases are classed as what?

Answer 9

Purines or pyramidines

Question 10

What are the properties of purine and what bases are purines?

Answer 10

Purines contain two interlocking nitrogen containing rings.

Purines are adenine and guanine.

Question 11

What are the properties of pyramidines and what bases are pyrimidines?

Answer 11

Pyrimidines contain a single nitrogen containing ring.

Pyrimidines are cytosine and thymine.

Question 12

How do nucleotides join together?

Answer 12

When nucleotides join together, a condensation reaction takes place and a phosphodiester bond is formed.

This occurs between the carbon of one nucleotide and the phosphate group of the nucleotide.

Question 13

In DNA, how are bases on different strands held together?

Answer 13

They are held together by H-bonds

Question 14

How many hydrogen bonds are required to join each DNA base pairings together?

Answer 14

Adenine always pairs with thymine by 2 hydrogen bonds.

Cytosine always pairs with guanine by 3 hydrogen bonds.

Question 15

What are the properties of the DNA double helix?

Answer 15

Two helical polynucleotide chains are coiled.

Complementary bases are held together by hydrogen bonds on the inside.

The individual hydrogen bonds are weak but the large number of them makes it stable.

Question 16

What does mitochondrial DNA do?

Answer 16

Encode the mitochondrial proteins and some ribosomal RNA.

Question 17

What does the mitochondrial DNA contain?

Answer 17

It contains genes to direct the synthesis of enzymes involved in oxidative phosphorylation (ATP production)

Contains genes for synthesis of transfer RNA (tRNA)

Contains genes for synthesis of ribosomal RNA (rRNA)
These RNA’S help assemble amino acids into functioning proteins.

Question 18

What is RNA?

Answer 18

RNA is a sequence of nucleotides.

Question 19

What are the fundamental differences between RNA and DNA?

Answer 19

1- RNA has a ribose sugar rather than deoxyribose

2- RNA is single stranded

3- Uracil instead of thymine

Question 20

Which RNA bases are purine and which ones are pyrimidines?

Answer 20

Purines in RNA = Adenine and guanine

Pyrimidines in RNA = Cytosine and uracil

Question 21

What is transcription?

Answer 21

Transcription- the production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule.

Question 22

What are the 4 steps of transcription?

Answer 22

1- Initiation
2- Elongation
3- Termination
4- Processing

Question 23

Explain the process of initiation?

Answer 23

The DNA molecule unwinds and separates to form a small open complex.

RNA polymerase (enzyme) binds to the promoter of the template strand.

Promoter regions- found at the beginning of the gene.

The promoter region contains sequences of thymine’s and adenine’s which is referred to as the TATA box.

TF = transcription factors- binds to the TATA box (promoter region) when signalled to.

RNA polymerase II is an enzyme that binds and opens up the DNA double helix and starts to read the information from the genetic code.

Question 24

Explain the process of elongation?

Answer 24

RNA polymerase II moves along the template strand, synthesising an mRNA molecule.

Question 25

Explain the process of termination?

Answer 25

Involves the addition of additional adenine nucleotides at the termination site of the RNA transcript.

The process of adding additional adenine nucleotides is called polyadenylation.

Question 26

Explain the process of processing?

Answer 26

Once transcription is terminated, the RNA molecule is then processed as follows:

Genes are composed of coding sequences (exons) interrupted by non-coding sequences (introns).

RNA splicing removes introns.

Messenger RNA (mRNA) is then produced which then leaves the nucleus through the nuclear pores.