Nucleic acids

Question 1

What is a TATA box?

Answer 1

This is a sequence of DNA which indicates to transcription factors where transcription begins. Located upstream from the start of transcription.

Question 2

What are CGP islands?

Answer 2

Stretches of DNA where there are multiple points at which C is followed by G. They are promoter regions which means that they are a region of DNA which Leeds to the initiation of transcription

Question 3

How do you ‘switch off’ a CpG island?

Answer 3

It is methylated

Question 4

How is Eukaryotic pre- mRNA processed?

Answer 4

1. ) Addition of a 5’ cap to the beginning of the RNA
2. )Addition of a poly A tail (tail of adenine nucleotides) to the end of RNA
3. )Splicing

Question 5

Why is a 5’ cap to the beginning of RNA?

Answer 5

The 5’ cap is added to the first nucleotide in the transcript- this is a modified guanine and it protects the transcript from being broken down. It also helps the ribosome to attach to thTe mRNA during translation.

Question 6

Why is poly A tail added?

Answer 6

When the polyadenylation signal shows up in the RNA molecule, an enzyme chops the RNA in two at this point. Another enzyme adds around 100-200 adenine nucleotides to the end cut forming a poly A tail.

This protects the mRNA from degradation and is involved in aiding the export of mature mRNA from the nucleus to the cytosol.

Question 7

What is splicing?

Answer 7

Specific parts of the pre- mRNA called introns are recognised and removed by a protein and RNA complex called a spliceosome. Introns are non coding sections hence they are not important and are removed. Exons are pasted together by spliceosome to make the final mature mRNA.

Question 8

What is a spliceosome?

Answer 8

A spliceosome is a large and complex molecular machine found primarily within the nucleus of eukaryotic cells. The spliceosome removes introns from a transcribed pre-mRNA, a type of primary transcript.

Question 9

What is prokaryotic mRNA described as?Why?

Answer 9

Polycistronic. This means that the mRNA can encode for more than one polypeptide

Question 10

What is the function of RNA polymerase 2?

Answer 10

Makes transcripts from the antisense (templates) strand of DNA

Question 11

How do we know DNA is the molecule of life?

Answer 11

• Griffith
• Avery
• Hershey and chase

Question 12

Describe the structure of DNA

Answer 12

• Antiparallel strands
• Has a double helix structure
• sugar phosphate backbone, phosphodiester bond linking adjacent deoxyribose sugars.
• Bases A,T,C,G

Question 13

Which bases are purines?

Answer 13

Adenine and guanine

Question 14

Which bases are pyrimidines?

Answer 14

Cytosine and Thymine

Question 15

Describe the larger scale packaging of DNA

Answer 15

DNA is coiled tightly with the help of histone proteins to form chromatin. Active genes are more loosely coiled as they are used more. Chromatin is condensed to form chromosomes

Question 16

Briefly describe what Griffiths experiments entailed

Answer 16

Looked at how information could be passed between cells, comparing different strains of disease by checking the effect of different strain of bacteria on mice. The mixing of the two strains together passed on whatever was causing the disease, showing something could be passed on.
• Avery later showed that ‘DNA was the transforming agent as out of purified DNA, RNA, protein, lipid and carbohydrate only DNA from heat killed virulent strain could induce virulence in the non-virulent strain’.

Question 17

What process is DNA replication?

Answer 17

Semi- conservative

Question 18

Why is DNA replication describes as semi- conservative?

Answer 18

Because of the two new DNA molecules formed, one strand contains an original strand and the other is newly synthesised DNA.

Question 19

What is site known as where DNA replication begins?

Answer 19

The origin of replication

Question 20

What direction does DNA replication occur?

Answer 20

5’ to 3’

Question 21

Describe the first stage of replication

Answer 21

Replication starts at a specific site called the origins of replication, DNA helices bind to this site and unwind the DNA which is done by breaking the hydrogen bonds between the nitrogenous bases.

Question 22

What is the error rate for mutations in the DNA?

Answer 22

-An error occurs about once every 100,000 nucleotides inserted into the growing strand of DNA (1 in 10^5).

• DNA polymerases have 3′ to 5′ editing function to remove incorrectly inserted bases. This reduces error frequency to around (1 in 10^7)
• A further check for mismatched bases by other enzymes helps to reduce the overall error frequency to (1 in 10^9) bases