Reassessment

Question 1

What is the base pairing rules?

Answer 1

DNA: A and T, G and C
RNA: A and U, G and C

Question 2

Explain the structure of DNA.

Answer 2

• 2 antiparallel strands, shaped as a double helix
• made up of nucleotides containing a phosphate deoxyribose sugar and a base
• 4 bases ATGC

Question 3

Where are linear and circular chromosomes found?

Answer 3

Circular - found in prokaryotes

Linear - found in eukaryotes

Question 4

What joins the fragments of DNA?

Answer 4

DNA ligase

Question 5

What are the steps of PCR?

Answer 5

Step 1: heating - 94 degrees, breaks bonds between bases, DNA unzips, strands separate

Step 2: annealing - 54 degrees, complementary primers bind to the strands of DNA

Step 3: extension- 72 degrees, taq polymerase binds to primers, extends them in 5’ to 3’ direction

This repeats around 30 times

Question 6

Describe the leading and lagging strand.

Answer 6

Leading - made continuously

Lagging - made in fragments which are then joined together

Question 7

What are the differences between the structures of DNA and RNA?

Answer 7

1. DNA has deoxyribose sugar, RNA has ribose
2. DNA has thymine, RNA replaces thymine with uracil
3. DNA is double stranded, RNA is single stranded

Question 8

What is RNA splicing?

Answer 8

• introns are removed from pre-mRNA, making the mature transcript

Question 9

What are introns and exons?

Answer 9

Introns - non coding regions
Exons - protein coding regions

During RNA splicing, INTRONS REMOVED, leaving exon to be translated.

Question 10

What happens at a ribosome during protein synthesis?

Answer 10

The ribosome is the site of protein synthesis

Question 11

What is the triplet code?

Answer 11

3 bases that code for an amino acid

Question 12

What does differentiation mean when referring to stem cells and meristems?

Answer 12

• when a cell develops more specialised functions for that type of cell

Question 13

What is the role of stem cells?

Answer 13

• stem cells have the ability to develop into different types of body cells during embryonic development
• they can either self renew or can differentiate into specialised cells (red blood cell, brain cell etc.)

Question 14

Give several ethical issues regarding stem cells.

Answer 14

For

• could potentially cure people with diseases like Alzheimer’s
• at 14 days old, the embryo hasn’t developed a nervous system or a brain
• bone marrow transplants
• drug testing
• skin grafts

Against

• embryo has the same rights and protection as the mother
• human life is sacred
• a unique piece of human DNA is created
• could potentially introduce cloning and will pursue natural selection
• in religious views, nobody should be playing God

Question 15

What does the word ‘genome’ mean?

Answer 15

• is the sum total of all the hereditary material within an organism

Question 16

What do non-coding sequences of DNA do?

Answer 16

1. Protection - some can telomere at the end of the chromosome which prevents ends from fraying
2. Non translated forms of RNA - tRNA, rRNA
3. Regulating transcription - they can bind to proteins which promote or prevent transcription

Question 17

What are the different types of single gene mutations? How would you recognise them?

Answer 17

1. Substitution - changes only one amino acid (or none at all)
2. Deletion - deletes an amino acid, normally effects every triplet (catastrophic)
3. Insertion - inserts an extra amino acid into the sequence

Question 18

What is the difference, in terms of protein produce, between substitution with a deletion or insertion?

Answer 18

Substitution - results in silent or misense mutations which produce the same amino acid or a different amino acid, they both produce the original protein in the end

Deletion and insertion - result in frame shift mutation, changes all the amino acids, results in a different or non functioning protein

Question 19

What are the 2 types of evolution and how to recognise each one?

Answer 19

Allopatric - occurs when a gene flow is physically prevented, geographical barriers (oceans etc.)

Sympatric - brought around by behavioural or ecological barriers, most common in plants, usually occurs within the same habitat

Question 20

What is genetic drift and how is it caused?

Answer 20

• the process of random changes in allele frequency in a population
• different to natural selection as it is random

Question 21

What are the names of the different domains of life?

Answer 21

1. Bacteria
2. Archaea
3. Eukaryotes

Question 22

What is the process of DNA replication?

Answer 22

Step 1: DNA polymerase breaks hydrogen bonds, unzips DNA

Step 2: the strands open in opposite directions, bases exposed

Step 3: primer is added to DNA, DNA polymerase adds nucleotides to 3’ end, DNA polymerase catalyses the formation of a strong chemical bonds between nucleotides (leading strand)

Step 4: primer added, DNA polymerase adds nucleotides to 3’ end, new primer is added, DNA polymerase extends this to meet the previous fragment of nucleotides, DNASE ligase joins them together, old primer replaced by DNA, process repeats until the strand is complete (lagging strand)

Question 23

What are prokaryotes and eukaryotes?

Answer 23

Prokaryotes - organisms that lack a membrane bound nucleus, DNA found in cytoplasm, bacteria

Eukaryotes - organisms that have a membrane bound nucleus that stores their DNA, animals plants and fungi