chapter 19- cellular control

Question 1

what is a mutation and give examples of some types

Answer 1

• it is a change in the base sequence in DNA, alters protein synthesis
• examples: substitution, deletion and insertion

Question 2

what is a point mutation

Answer 2

• only one nucleotide affected

Question 3

mutations may occur spontaneously in cell division or be caused by mutagenic agents
list physical mutagens

Answer 3

-uv light
-x rays
-gamma rays

Question 4

list chemical mutagens

Answer 4

benzopyrene found in tobacco smoke
mustard gas
colchicine
nitrous gas
aromatic amines found in synthetic dyes
free radicals

Question 5

list biological mutagens

Answer 5

charred meat
alcohol
some viruses
transposons- remnants of viral nucleic acid incorporated into our genome
aflatoxins found in contaminated nuts
mycotoxins from fungi

Question 6

definition of a transcription factor

Answer 6

molecule that can bind to Dna and either initiate or inhibit transcription. these molecules move from cytoplasm to nucleus and bind to DNA.

Question 7

what biological molecule are transcription factors

Answer 7

-proteins so have a complementary shape to a binding site on the DNA molecule.

Question 8

how do transcription factors initiate transcription

Answer 8

complementary shape to dna binding site and so binding of transcription factor enables rna polymerase to bind and transcription to take place.

Question 9

how does the absence of a transcription factor prevent the protein from being made.

Answer 9

without the binding of a transcription factor, the gene is inactive and transcription cannot take place.protein cannot be made

Question 10

how may a transcription factor inhibit transcription

Answer 10

binding of transcription factor to dna binding site on gene may prevent rna polymerase from binding and transcription from taking place.

Question 11

definition of an operon

Answer 11

a group of simultaneously controlled genes that are either all expressed or are all not.

Question 12

are operons found in eukaryotic or prokaryotic cells

Answer 12

operons are more common in prokaryotes than in eukaryotes.

Question 13

what prokaryote is lac operon found in

Answer 13

-e coli

Question 14

lac operon definition

Answer 14

a group of three structural genes, lac a, lac y and lac z that are responsible for lactose metabolism.

Question 15

why do bacteria metabolise lactose

Answer 15

bacteria require less energy to metabolise glucose than lactose in respiration, so glucose is the favourable respiratory substrate, however if glucose isn’t present lactose will be digested.

Question 16

when are the proteins produced by the lac operon for lactose metabolism needed

Answer 16

-only needed when glucose is absent and lactose is present
this regulates the transcription of these genes to meet demand.

Question 17

what is lac l and what is its function

Answer 17

lac l is a regulatory gene found near the operon. it codes for the repressor protein that inhibits transcription when lactose is absent.

Question 18

what happens when lactose is absent
is transcription inhibited or initiated

Answer 18

the repressor protein is constantly produced and binds to the operator (a region close to the operon) which prevents rna polymerase from binding to the promoter (dna binding site) and transcription is inhibited.

Question 19

what happens when lactose is present
is transcription inhibited or initiated

Answer 19

when lactose is present it binds to the repressor protein, this changes the shape of the repressor protein and so it can no longer bind to the operator and therefore the rna polymerase can bind to the promoter region and transcription can take place.

Question 20

what increases the rate of transcription of the lac operon

Answer 20

in order for sufficient enzymes to be produced, lac y lac a and lac z camp receptor protein CRP must bind. CRP can only bind and increase transcription rate if it is bound to camp.

Question 21

what does CRP stand for

Answer 21

camp receptor protein

Question 22

what is the definition of epigenetics

Answer 22

a heritable change in gene function, without changing the dna base sequence
these changes are caused by changes in the environment and can inhibit transcription or initiate transcription

Question 23

does methylation inhibit or initiate transcription and how does it do so

Answer 23

increased methylation inhibits transcription
when methyl groups are added, they are attached to the cytosine base. methyl groups have a positive charge. There is an attraction between a positive methyl and the negatively charged phosphate groups. this causes a stronger attraction between histone and the dna. this results in tight coiling of DNA, resulting in transcriptional factors being unable to bind to the gene.

Question 24

does acetyl group to histone proteins inhibit or initiate transcription

Answer 24

acetyl groups are negatively charged and bind to the histone proteins. phosphate groups of dna are negatively charged. these forces repel, causing looser coiling of dna (euchromatin).
transcription factors are able to access the gene, and RNA polymerase can bind to the gene and so transcription can occur

Question 25

what will increased methylation and decreased acetylation do to transcription

Answer 25

-inhibits transcription, prevents transcription factors from binding to the gene and rna polymerase cannot bind and so transcription cannot occur

Question 26

what will decreased methylation and increased acetylation do to transcription

Answer 26

-increase transcription as heterochromatin converted to euchromatin which is loosely coiled and so transcription factors can access the gene and rna polymerase can bind and so transcription can occur.

Question 27

what is the coiling of the dna dependent on

Answer 27

the attraction between the negatively charged phosphate groups of the dna and the positively charged histone proteins. when this attraction increases the dna coils more tightly, when there is a greater repulsion between histone proteins and phosphate groups, dna coils less tightly (euchromatin)