chapter 19- cellular control Flashcards
what is a mutation and give examples of some types
- it is a change in the base sequence in DNA, alters protein synthesis
- examples: substitution, deletion and insertion
what is a point mutation
- only one nucleotide affected
mutations may occur spontaneously in cell division or be caused by mutagenic agents
list physical mutagens
-uv light
-x rays
-gamma rays
list chemical mutagens
benzopyrene found in tobacco smoke
mustard gas
colchicine
nitrous gas
aromatic amines found in synthetic dyes
free radicals
list biological mutagens
charred meat
alcohol
some viruses
transposons- remnants of viral nucleic acid incorporated into our genome
aflatoxins found in contaminated nuts
mycotoxins from fungi
definition of a transcription factor
molecule that can bind to Dna and either initiate or inhibit transcription. these molecules move from cytoplasm to nucleus and bind to DNA.
what biological molecule are transcription factors
-proteins so have a complementary shape to a binding site on the DNA molecule.
how do transcription factors initiate transcription
complementary shape to dna binding site and so binding of transcription factor enables rna polymerase to bind and transcription to take place.
how does the absence of a transcription factor prevent the protein from being made.
without the binding of a transcription factor, the gene is inactive and transcription cannot take place.protein cannot be made
how may a transcription factor inhibit transcription
binding of transcription factor to dna binding site on gene may prevent rna polymerase from binding and transcription from taking place.
definition of an operon
a group of simultaneously controlled genes that are either all expressed or are all not.
are operons found in eukaryotic or prokaryotic cells
operons are more common in prokaryotes than in eukaryotes.
what prokaryote is lac operon found in
-e coli
lac operon definition
a group of three structural genes, lac a, lac y and lac z that are responsible for lactose metabolism.
why do bacteria metabolise lactose
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.
when are the proteins produced by the lac operon for lactose metabolism needed
-only needed when glucose is absent and lactose is present
this regulates the transcription of these genes to meet demand.
what is lac l and what is its function
lac l is a regulatory gene found near the operon. it codes for the repressor protein that inhibits transcription when lactose is absent.
what happens when lactose is absent
is transcription inhibited or initiated
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.
what happens when lactose is present
is transcription inhibited or initiated
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.
what increases the rate of transcription of the lac operon
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.
what does CRP stand for
camp receptor protein
what is the definition of epigenetics
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
does methylation inhibit or initiate transcription and how does it do so
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.
does acetyl group to histone proteins inhibit or initiate transcription
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
what will increased methylation and decreased acetylation do to transcription
-inhibits transcription, prevents transcription factors from binding to the gene and rna polymerase cannot bind and so transcription cannot occur
what will decreased methylation and increased acetylation do to transcription
-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.
what is the coiling of the dna dependent on
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)
