GENETIC INFO IN DNA AND REPLICATION

Question 1

Give 4 differences between RNA and DNA

Answer 1

DNA:
- Double-stranded
- Contains thymine
- Larger in size
- Has only a H at the 2 position

RNA:
- Single-stranded
- Smaller in size
- Has Uracil instead of thymine
- Has an OH group at the 2 position

Question 2

What is the difference between thymine and uracil?

Answer 2

Thymine contains a CH3 group that uracil doesn’t have

Question 3

What is the name of the bonds formed between nucleotides?

Answer 3

Phosphodiester bonds

Question 4

Which is unstable and which is stable between DNA and RNA and why?

Answer 4

DNA = stable
RNA = unstable

RNA is unstable because the LP electrons on the OH group react with the phosphate group on another RNA molecule. It is unstable because it may need to change expression patterns. DNA doesn’t have an OH group at C2, only H

Question 5

Which bases are purines?

Answer 5

Adenine and Guanine

Question 6

Which bases are pyrimidines?

Answer 6

Cystosine and thymine

Question 7

In which direction do DNA strands run in and from which ends?

Answer 7

• Antiparallel
• 5’ to 3’

Question 8

Chromosome?
Gene?

Answer 8

Chromosome = single molecule of DNA
Gene = specific stretch of DNA which contains a specific sequence that contains genetic instructions. Each chromosome has hundreds of genes

Question 9

What are introns and exons?

Answer 9

Introns = non coding DNA (removed via splicing)
Exons = Coding DNA

Question 10

What are mini satellites and what are micro satellites?

Answer 10

They are types of tandem repeats in a gene

MINI = Up to 1000 copies in one block and can be found at telomeres

MICRO = Small arrays of simple sequence repeats and these are usually non coding

Can identify people based on how many repeats they have

Question 11

What is the role of repeat sequences at the:

• telomeres
• centromeres

Answer 11

Telomeres = allows replication to the tip of chromosomes

Centromeres = essential for segregation during cell division. The proteins that are involved in cell division, bind to the centromeres sequences

Question 12

Give 3 problems that can be caused at repeat sequences

Answer 12

Telomeres = unstable and deletions can occur below the telomeres

Mini satellites = large scale duplication/ deletion between homologous chromosomes or translocation of DNA between non - homologous chromosomes

Question 13

Definitions of EUCHROMATIN and HETEROCHROMATIN (chromatin found in the nucleus)

Answer 13

EUCHROMATIN - prevalent in gene-rich areas and are less compact so proteins that are involved in transcription can access them easily

HETEROCHROMATIN = Condensed chromatin found in an interphase chromosome. Not gene-rich and not transcriptionally active. Can be found in the condensed and uncondensed form

Question 14

What effect does ultraviolet radiation have on DNA?

Answer 14

Causes thymine dimers

Question 15

What is a nucleosome?

Answer 15

Beadlike structural unit composed of DNA wound around a core of histone proteins

Question 16

what mechanisms do cells have to repair errors?

Answer 16

Mismatch repair systems - these minimise the introduction of mutations

Question 17

What can mismatching in DNA result in?

Answer 17

DNA not pairing properly

Question 18

What is deprivation?

Answer 18

Losing a base - this effects the template for the next division

Question 19

What is deamination?

Answer 19

Cytosine becomes uracil - this results in problems with base pairing