chapter 19 - genetics of living systems

Question 1

what is a mutation

Answer 1

a change in the sequence of bases in DNA

Question 2

what is a mutation caused by

Answer 2

substitution, deleting or insertion of one or more nucleotides within a gene

Question 3

what does the substitution of a nucleotide cause

Answer 3

codon changes so a different amino acid is produced which changes primary structure of protein or different position of R group affecting function

Question 4

what does insertion or deletion of a nucleotide cause

Answer 4

leads to a frameshift mutation

Question 5

what are the effects of different mutations

Answer 5

no effect on phenotype as normal proteins are synthesised
damaging phenotype because proteins are non functional
beneficial as a new useful characteristic is produced

Question 6

what are the causes of mutations

Answer 6

occurs randomly during DNA replicationbut rate of mutation is sped up by mutagens
depurination or depyrimidination leading to insertion of incorrect base
free radicals

Question 7

what is a mutagen

Answer 7

chemical, physical or biological agent which causes mutations

Question 8

what are silent mutations

Answer 8

mutations that do not change protein function but may still affect primary structure

Question 9

what are nonsense mutation

Answer 9

results in codon becoming a stop coding which results in shortened non-functional protein

Question 10

what are missense mutations

Answer 10

results in the incorporation of an incorrect amino acid into the primary structure. can be harmless ( conservative) or dangerous ( non-conservative ) or beneficial

Question 11

what is an example of a beneficial mutation

Answer 11

ability to digest lactose preventing diseases such as osteoporosis

Question 12

what is sickle-cell anaemia

Answer 12

blood disorder where erythrocytes develop abnormally causesd by mutation in gene coding for haemoglobin.

Question 13

what base is substituted in sickle-cell anaemia

Answer 13

adenine replaced by thymine making 6th amino acid, valine instead of glutamic acid on beta haemoglobic chain

Question 14

what are changes in chromosome structure

Answer 14

deletion
duplication
translocation - section of one chromosome breaks off and joins another non-homologous chromosome
inversion - section of chromosome breaks off , is reversed, and then joins back onto the chromosome

Question 15

what genes form enzymes in metabolic pathways

Answer 15

house keeping genes

Question 16

what genes form protein based hormones

Answer 16

tissue -specific genes

Question 17

how are genes regulated

Answer 17

transcriptional - genes turned on or off
post-transcriptional - mRNA modified which regulates translation and types of protein produced
translational - translation stopped or started
post-translational - proteins modified after synthesis to change their function

Question 18

what is heterochromatin

Answer 18

tightly wound DNA causing chromosomes to be visible during cell division

Question 19

what is euchromatin

Answer 19

loosely wound DNA present during interphase

Question 20

how are transcription of genes prevented

Answer 20

DNA is tightly wound ( heterochromatin) so RNA polymerase cannot access the gene

Question 21

why does DNA coil around histones

Answer 21

DNA is negatively charged and histones are positively charged

Question 22

how does acetylation and phosphorylation allow genes to be transcribed

Answer 22

reduces positive charge on histones so DNA coils less tightly so genes can be transcribed

Question 23

how does methylation prevent transcription of genes

Answer 23

makes histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly

Question 24

what are epigenetics

Answer 24

control of gene expression by modification of DNA

Question 25

what is an operon

Answer 25

a group of genes that are under the control of the same regulatory mechanism

Question 26

what is lac operon

Answer 26

a group of 3 genes, lacZ lacY and lacA involved in metabolism of lactose. They are structural genes as they code for 3 enzymes ( b-galactosidase, lactose permease, transacetylase) and they are transcribed onto a single mRNA

Question 27

what is a regulatory gene

Answer 27

lacI is located near operon and codes for repressor protein that prevents transcription of structure genes in absence of lactose

Question 28

what is down regulation

Answer 28

repressor protein binds to the operator which prevents RNA polymerase binding to DNA ( promoter) and beggining transcription as 3 structural genes are not transcribed

Question 29

what is the role of cAMP

Answer 29

increases rate of transcription for enzymes needed to metabolise lactose

Question 30

what does glucose do to cAMP

Answer 30

decreases levels of cAMP to reduce transcription of genes for metabolism of lactose

Question 31

what is the product of transcription

Answer 31

pre-mRNA which is modified to mature mRNA to bind to ribosome for synthesis

Question 32

what is a cap

Answer 32

modified nucleotide

Question 33

what is a tail

Answer 33

a long chain of adenine nucleotides

Question 34

how are mRNA stabilised

Answer 34

a cap is added to the 5 end and tail added to 3 end which delays degradation in cytoplasm