topic 7

Question 1

genome

Answer 1

all the genetic information within a cell

Question 2

PCR - what is it

Answer 2

• makes large number of copies of DNA fragments - amplifying DNA

Question 3

how does PCR work

Answer 3

1. reactants are mixed and placed in the PCR machine
   - DNA sample
   - DNA primers
   - 4 nucleotide bases
   - taq DNA polymerase
   - pH buffer
2. heated at 90-95C for 30 seconds - DNA strand separates
   - DNA unzips due to breakage of hydrogen bonds
3. 50-55C for 20 seconds - primers bind to DNA strands (annealing)
4. 72C for 1 minute minimum - DNA polymerase builds up complementary strands of DNA
   - DNA polymerase creates a copy of the sample by complementary base pairing (elongation)
5. repeated 30 times - 1 billion copies made in 3 hrs

Question 4

taq DNA polymerase - why is it added?

Answer 4

• when heated to 90C to unzip the DNA, DNA polymerase gets denatured and DNA can’t replicate
• taq polymerase is able to withstand high temperatures (as it is made from bacteria which live in hot conditions) so won’t denature

Question 5

using DNA sequences

Answer 5

• predicting amino acid sequences
• uses genetic code - not all DNA sequences are translated so it is not certain
• particular sequences linked to disease or increased likelihood of disease can be identified in individuals

Question 6

gene sequencing process

Answer 6

• DNA strands are chopped into smaller pieces
• double strands are separated into single strands
• PCR is involved in replicating the DNA fragments to produce large quantities of materials for analysis
• labelled terminator bases are added to the single strands of DNA
• coloured tags enable the sequence of bases to be read rapidly by an automatic system

Question 7

what are terminator bases

Answer 7

• modified version of one of the four nucleotide bases
• when a terminator base is incorporated, the chain is halted and no more bases can be added

Question 8

DNA profiling

Answer 8

• identifies individuals or relationships
• uses the fact that restriction enzymes cut an individual DNA into fragments in a way that is unique
• fragments are separated by electrophoresis
• gives a pattern/profile that can be compared with forensic samples or relatives

Question 9

gel electrophoresis

Answer 9

• fragments placed in wells in gel
• dyed with ethidium bromide - to become visible under UV light
• current applied to the gel
• DNA is negative so fragments of different sizes move at different speeds

Question 10

what are transcription factors

Answer 10

• proteins that bind to DNA
• either stimulate or prevent transcription of DNA

Question 11

what is meant by gene expression

Answer 11

• when the protein coded for by a gene is produced / synthesised (via transcription & translation)

Question 12

how are genes expressed

Answer 12

• when mRNA is actively produced using the gene’s base sequence in transcription
• mRNA then carries the code to produce a specific sequence of amino acids in a polypeptide

Question 13

what are polypeptides used for

Answer 13

• used to produce proteins, some of which control cellular activity

Question 14

why do cells differ from eachother

Answer 14

• each cell type expresses a different group of genes

Question 15

what is differentiation

Answer 15

• the process by which certain groups of genes are activated to produce a particular cell type

Question 16

where to transcription factors bind

Answer 16

• promoter regions
• enhancer regions

Question 17

promoter regions

Answer 17

• found next to the gene they act on (5’)
• promoter regions enable binding of RNA polymerase at the gene

Question 18

enhancer regions

Answer 18

• make the gene more accessible
  changes to the chromatin structure
• open chromatin -> gene expressed. more accessible to RNA polymerase so more transcription occurs
• closed chromatin -> gene is not expressed

Question 19

examples of transcription factor control

Answer 19

• development
• hormonal control
• control of the cell cycle
• pathogens controlling host cells

Question 20

development

Answer 20

• the organisation of a developing embryo relies heavily on TFs to govern gene activity in forming different tissues and organs

Question 21

hormonal control

Answer 21

• cells affected by oestrogen have a receptor molecule which binds to form a complex to activate specific genes

Question 22

control of the cell cycle

Answer 22

• changes in a dividing cell and also when a cell can divide are controlled by TFs

Question 23

pathogens controlling host cells

Answer 23

• some bacteria produce TFs which modify gene expression in host nuclei