8. Control of Gene Expression

Question 1

Gene mutation

Answer 1

change in the base sequence of DNA, occurs during DNA replication (eg. addition, deletion, substitution, inversion, duplication and translocation)

Question 2

Substitution

Answer 2

one base is replaced by another, triplet may still code for the same amino acid as DNA is degenerate

Question 3

Deletion

Answer 3

one base is removed, causes a frame shift which alters all subsequent triplets

Question 4

Inversion

Answer 4

a sequence of bases are reversed

Question 5

Duplication

Answer 5

a sequence of bases are repeated, causes a frame shift which alters all subsequent triplets

Question 6

Translocation

Answer 6

a sequence of bases are moved from one part of the genome to another

Question 7

Mutagenic agents

Answer 7

factors that increase rate of mutations (eg. UV radiation, ionising radiation), they can substitute for a base (base analogs), delete bases or change DNA structure

Question 8

Tumour

Answer 8

a mass of cells as a result of uncontrolled cell division, can be benign (non-cancerous) which grow slower or malignant (cancerous) which grow faster and can metastasise/spread

Question 9

Tumour suppressor gene

Answer 9

produce proteins that slow rate of cell division and cause apoptosis

Question 10

Proto-oncogene

Answer 10

produce proteins that speed up rate of cell division and inhibit apoptosis

Question 11

Stem cells

Answer 11

unspecialised cells that can divide and differentiate into specialised cells, all genes in an embryonic stem cell can be expressed (transcribed and translated)

Question 12

Totipotent stem cells

Answer 12

can differentiate into any body cell, found in early mammalian embryos

Question 13

Pluripotent stem cells

Answer 13

can differentiate into almost any body cell, found in embryos

Question 14

Multipotent stem cells

Answer 14

can differentiate into few types of body cell, found bone marrow

Question 15

Unipotent stem cells

Answer 15

can differentiate into one type of body cell, found in adult organ tissues

Question 16

iPS cells

Answer 16

induced pluripotent stem cells using a virus as a vector which inserts transcription factors from pluripotent stem cells into the DNA of unipotent adult somatic cells, helps overcome ethical issues of using embryonic stem cells

Question 17

Transcription factors

Answer 17

proteins that move from the cytoplasm to the nucleus, bind to specific promoter regions on DNA, helping RNA polymerase bind, activating transcription

Question 18

Oestrogen

Answer 18

diffuses through phospholipid bilayer into cytoplasm, binds to oestrogen receptor transcription factor, oestrogen-oestrogen receptor complex binds to specific promoter region on DNA, helping RNA polymerase bind, activating transcription

Question 19

Epigenetics

Answer 19

heritable changes in gene expression without changing the base sequence of DNA

Question 20

Methylation

Answer 20

methyl groups (CH3) attach to DNA at CpG sites, preventing RNA polymerase binding, preventing transcription

Question 21

Acetylation

Answer 21

acetyl groups attach to histones, making them space out, DNA is less tightly coiled allowing RNA polymerase to bind, allowing transcription

Question 22

RNA interference

Answer 22

small double stranded RNA molecules prevent translation of mRNA

Question 23

siRNA

Answer 23

associates with proteins to form an siRNA-protein complex, unwinds becoming single stranded, binds to target mRNA by complementary base pairing, breaks down target mRNA into fragments, preventing translation, mRNA fragments are recycled

Question 24

miRNA

Answer 24

associates with proteins to form an miRNA-protein complex, unwinds becoming single stranded, binds to target mRNA by complementary base pairing, prevents ribosome binding, preventing translation

Question 25

Genome

Answer 25

complete set of genes in a cell

Question 26

Proteome

Answer 26

full range of proteins a cell is able to produce, in complex organisms the proteome cannot be easily determined due to lots of non-coding DNA and regulatory genes

Question 27

Genome sequencing

Answer 27

mapping the full sequence of an organism’s genome (eg. The Human Genome Project), allows us to identify genes causing inherited diseases rapidly

Question 28

Recombinant DNA technology

Answer 28

involves transferring DNA fragments from one organism to another, since the genetic code is universal the transferred DNA can be translated into a protein in recipient cells

Question 29

Producing DNA fragments

Answer 29

use reverse transcriptase, restriction endonucleotases or a gene machine

Question 30

Reverse transcriptase

Answer 30

makes a complementary strand of DNA (cDNA) from mRNA template

Question 31

Restriction endonucleases

Answer 31

bind to specific palindromic sites on DNA either side of the target gene, cutting into DNA fragments, leaving sticky ends

Question 32

Gene machine

Answer 32

creates oligenonucleotides and joins them together to create DNA fragments using a computerised machine

Question 33

Amplifying DNA fragments

Answer 33

use in vivo or in vitro cloning

Question 34

In vivo cloning

Answer 34

using bacteria to create a large number of copies of a DNA fragment

Question 35

Transforming cells

Answer 35

add a marker gene, promoter region and terminator region to the DNA fragment, isolate plasmid and cut with restriction endonucleotase, leaving sticky ends, mix plasmid and DNA fragment with ligase, joining sticky ends, forming recombinant DNA, insert recombinant DNA into vector and identify using marker genes that code for antibiotic resistance or UV fluorescence, select and culture transformed vectors

Question 36

In vitro cloning

Answer 36

using PCR to create a large number of copies of a DNA fragment

Question 37

PCR

Answer 37

set up reaction mixture containing DNA fragment, DNA polymerase, DNA nucleotides and primers, heat to 95°C to break hydrogen bonds between complementary base pairs, cool to 50°C so primers can bind to DNA by complementary base pairing, heat to 70°C so DNA polymerase joins adjacent nucleotides, forming phosphodiester bonds

Question 38

Somatic gene therapy

Answer 38

changing the alleles in body cells to treat genetic disorders, if caused by two recessive alleles a dominant allele is inserted, if caused by a dominant allele the dominant allele is silenced

Question 39

Germ line gene therapy

Answer 39

changing the alleles in gametes so offspring won’t suffer from the genetic disorder

Question 40

DNA probes

Answer 40

short single strands of DNA bases complementary to a specific allele

Question 41

Locating specific alleles

Answer 41

extract DNA and add restriction endonucleases, separate fragments using gel electrophoresis, treat DNA to form single strands, attach a label to the DNA probe, DNA probe hybridises and sticks to the DNA fragment by complementary base pairing, rinse to remove unbound DNA probes, view labels under UV light

Question 42

DNA microarray

Answer 42

attach a label to the DNA fragment, add to a glass tile with many DNA probes attached to screen for multiple alleles

Question 43

Personalised medicine

Answer 43

locating specific alleles can help identify inherited conditions, health risks and determine response to specific drugs

Question 44

Genetic counsellors

Answer 44

use screening results to advise the patient and their family about risks of the genetic disorder and suggest effective treatments

Question 45

Genetic fingerprinting

Answer 45

identification of individuals by comparing differences in VNTRs, can be used in forensics, medical diagnosis and conservation of endangered species

Question 46

Genetic fingerprinting process

Answer 46

extract DNA fragment from sample, cut using restriction endonucleases, amplify using PCR, separate DNA fragments by gel electrophoresis, add DNA probe with fluorescent or radioactive label, view under UV light or X-ray, shorter DNA fragments move further, if two bands reach the same location on the gel they have the same number of nucleotides and thus VNTRs