4) Genetics

Question 1

Cytarabine prevents DNA replication. Explain why it has a greater effect on cancer cells than on healthy cells

Answer 1

Cancer cells replicate faster and uncontrollably

Question 2

Tube A has a band at the top, tube B has a band at the bottom. Explain why.

Answer 2

Tube A is less dense and Tube B is more dense

Question 3

There is one band in the middle of the tube. Explain why

Answer 3

There is DNA with one heavy strand and one light strand. The new strand is made with 14N

Question 4

Why is DNA a polymer

Answer 4

It contains repeating units of a phosphate group, deoxyribose sugar and nitrogenous organic base

Question 5

A polypeptide has 51 amino acids. What’s the minimum number of DNA bases required to code for the amino acids in this polypeptide

Answer 5

51 x 3 = 153

Question 6

The gene for this polypeptide contains more than the number of bases. Explain why

Answer 6

Some regions of the gene are non coding introns.

Question 7

Strand of DNA has
ACA/CAUGAA/UGCUAG
Exon/intron/exon. Give the sequence of bases on the mRNA produced by splicing the pre-mRNA

Answer 7

UGU UGC UAG

Question 8

Describe and explain how the structure of DNA results in accurate replication (4)

Answer 8

DNA contains two strands. Semi conservative replication is possible.
Hydrogen bonds hold the strands together
The hydrogen bonds are weak to separate the strands
The bases are exposed and act as a template
AT GC. Complimentary copy
DNA contains one original and one new strand

Question 9

Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells. (7)

Answer 9

• chromosomes shorten and thicken
• chromosomes each become two identical chromatids
• chromatids move to equator (middle of spindle)
• chromatids attach to individual spindle fibres
• simple fibres shorten and centromeres divide
• chromatids separate and move to opposite poles of the spindle
• each pole has identical copies of chromosomes
• nuclear envelope forms around each set of chromosomes
• cytokinesis occurs, cytoplasm divides into two new identical cells

Question 10

What are the stages of mitosis? (5)

Answer 10

Interphase, prophase metaphase, anaphase, telophase. IPMAT!!

Question 11

Describe what happens in prophase

Answer 11

• each chromosomes are two identical chromatids
• Chromosomes shorten become thicker
• Nuclear envelope breaks down
  Protein fibres form a spindle in the cell

Question 12

Describe what happens in metaphase

Answer 12

• spindle fibres attach to centromere of each chromatids

- chromosomes line up in the middle of equator

Question 13

Describe what happens in anaphase

Answer 13

• Spindle fibres shorten
• centromeres divide and move to opposite poles of spindle
  Chromatids - chromosomes

Question 14

Describe what happens in telophase

Answer 14

• two sets of chromosomes on opposite ends of cell
• nuclear envelope forms around each set
• cytokinesis produces two new identical cells

Question 15

Define cytokinesis

Answer 15

Cytoplasm division in mitosis

Question 16

Which of these three contain hydrogen bonds. DNA tRNA mRNA

Answer 16

DNA and tRNA

Question 17

How many polynucleotide strands does DNA, mRNA & tRNA have?

Answer 17

1 - mRNA, tRNA

2 - DNA

Question 18

Explain why replication of DNA is described as semi-conservative (2)

Answer 18

Each strand copied acts as a template.

DNA has one new strand and one original strand

Question 19

Explain how the structure of DNA relates to its functions (6)

Answer 19

Helix and coiled so it’s compact and can be stored in small spaces.
Double stranded for semi conservative replication.
weak hydrogen bonds for replication and unzipping.
Many hydrogen bonds which are strong.
Long and large molecule and can store lots of information.
Base sequence where stored information codes for amino acid of proteins.
Sugar phosphate backbone provides strength.

Question 20

Describe selection

Answer 20

There is a mutation in alleles which causes a variation within a species. Some have the advantageous allele to survive and reproduce to pass on the allele
There is an increase in frequency of advantageous alleles, leading to survival and a decrease in frequency of non-advantageous alleles, so they die.

Question 21

Describe how DNA is replicated

Answer 21

DNA helicase separates DNA strands by breaking hydrogen bonds between them. Both strands act as template for free nucleotides to attach by complimentary base pairing. DNA polymerase joins nucleotides together and hydrogen bonds reform producing two new DNA molecules containing one old strand and one new stand by semi conservative replication