chapter 19- genetics of living systems Flashcards
what is a mutation
a sudden, significant, random change in the dna of a cell (change in the base sequence of DNA)
a stable heritable change in genetic material.
they introduce an unpredictable form of variation and can lead to the formation of new genes
do mutations occur in all groups of living things
yes
a mutation may be restricted to …… or may even affect a …….. in a cell
a single gene or a number of chromosomes in a cell
what does it mean if a mutation occurs in a somatic cell
somatic mutations are not in gametes and so only affect the organism and cannot be inherited
only true of multicellular organisms
what are germ-line mutations
mutations that occur in gametes and so may be transmitted to future generations in the future
only true of multicellular organisms
Gene mutation occurs spontaneously during DNA replication. However, some external factors can increase the rate of mutation. these factors are called…
mutagenic agents
what are the mutagenic agents
viruses
chemicals
radiation (different types have different effects on living cells depending on the wavelength and dose of radiation)
how and why can a mutation be passed on
if a new gene results from a mutation and confers some form of selective advantage, then when the organism reaches maturity and get a mate it will be more likely to be passed on
over time mutation increases in frequency in the gene pool
what is the effect of radiation on fruit flies eg
radiation will cause a mutation causing vestigial wings
give an example of when a mutation can have a beneficial advantage
and exp
sickle cell anaemia
inherited mutation of a gene that codes for the structure of haemoglobin, causing the rbcs to become sickle shaped (when they encounter low conc of O2)
causing severe pain (rbcs become lodged in capillary beds) and tiredness
in tropical africa mutation gives resistance to a severe form of malaria, therefore mutation was passed on
how is sickle cell anaemia caused
it is as a result of a gene mutation the mutated gene (haemoglobin S) is recessive
so only homozygous recessives suffer
how is the is a rbc changed in shape
there is a base substitution on the dna sense strand which now codes for abnormal Hb, that changes the mrna strand as it is complementary which results in a different protein being produced as a result and so the Hb molecule has an abnormal shape
What is a substitution mutation?
A substitution mutation is when a nucleotide is swapped out for a different one - a point mutation, the other nucleotide contains a different base
occurs as an error during dna replication
only one base codon is affected > one aa changed at specific position within the final polypeptide
can have a minor or serious consequence if the proteins shape is affected
examples of conditions which result from point mutations
sickle cell anaemia (sub)
cystic fibrosis
colour blindness (red/green) - sexlinked
some cancers (base sub in tumor suppressor genes)
these are differences in the phenotype
explain why colour blindness is more common in males than females (2)
it is caused by a recessive allele on the x chromosome
males only need one recessive allele and females need two recessive alleles to be colour blind
what are the 3 results of point/sub mutations
silent (dk it occurs), nonsense > stop = codes for nothing (cant make rest of the protein), missense (conservative/non)(has different 3d shape)
why would a base substitution in a dna triplet may not alter the amino sequence of a protein
because the genetic code is degenerate as there is more than one codon for most of the amino acids so it will still code for the same amino acid
What is a deletion mutation? and what does it result it
A deletion mutation is when a nucleotide is removed from a DNA sequence (usually irreversible, unlikely to be undone by an insertion)
causes frame shift > altering all of the base triplets downstream from the mutation within the reading frame (more impact potentially every aa after mut will be different)
greatest effect on the structure of the protein, often leads to the formation of non-functional proteins
what happens when 3 bases are deleted
it doesnt alter the reading frame but does result in the loss of an amino acid from the final polypeptide chain
What is an insertion/addition mutation? and what are they caused by
An insertion mutation is when a nucleotide is added to a DNA sequence
caused by errors during replication of repeating elements (rg AT repeats) or caused by transposable elements (therefore they can be reversed by excision of the TE)
if the genetic information transported from the dna to the ribosomes for protein synthesis by mutation then the …. structure is altered
what other structure is also altered
primary
tertiary and
quaternary (potentially)
what is albinism and how is it caused
inability of cells to form the pigment melanin because a mutation of the gene that codes for an enzyme involved in the chemical pathway leading to melanin results in the loss of the enzyme
what disadvantages comes with albinism
lack of camouflage > death
lack of UV protection > death
die before maturity so not an advantage and more likely to not pass on gene so not that common
Which types of gene mutation lead to frameshift?
insertion
deletion
not sub cus it only changed one single nucleotide. at most it would change the aa one triplet codes for, it wouldt cause a change in the entire sequence of base triplets
What is a frameshift?
A frameshift is a change in the sequence of base triplets in a gene.
What are the possible effects of mutation on proteins?
Mutations which change a protein’s primary structure also alter the bonds within its tertiary structure.
This may result in a non-functioning protein, which may be harmful to the organism.
Alternatively, the change may result in a new protein, which could be beneficial to the organism.
cells can switch genes on and off in order to ….
conserve the cells resources
at any one time only about 5% of cells genes are being expressed
transcription in a nutshell
occurs in the nucleus of a cell and involves the formation of a messenger RNA molecule that carries a complementary DNA message to the ribosomes in the cytoplasm
translation in a nutshell
occurs at the ribosomes in the cytoplasm and involves the translation of the MRNA message into a specific sequence of amino acids to form a polypeptide/protein
what are the 3 ways that RNA is structurally different from DNA
RNA had uracil in place of thymine in DNA
RNA contains ribose in place of deoxyribose in DNA.
RNA is usually single stranded whereas DNA is a double stranded helix
Within a gene, what is an intron?
An intron is a base sequence in a gene that is non-coding.
gene expression can be controlled at either the …. stage or the ….. stage
transcription or translation stage
what are the 4 categories in that gene expression can occur
transcriptional
post transcriptional
translational
post translational
what happens in the transcriptional category for gene expression
the process of transcription is prevented so mRNA is not synthesised
in the transcriptional regulation of gene expression what in involved? the removal of ….
the removal of all the introns from the pre mRNA (that do not code for proteins)
this occurs in the nucleus and then the mature mRNA is produced as a result
what happens in the post transcriptional category for gene expression/What changes happen during post-transcriptional control?
the mRNA is controlled/regulated after if has been synthesised
changes are made to mRNA after transcription.
what happens in the translational category for gene expression
the process of translation is prevented
what happens in the post translational category for gene expression/What changes happen during post-translational control?
the polypeptide is modified after it has been synthesised/after translation
Proteins are not usually functional after translation.
Proteins must be …. before they are ready to perform specific functions.
activated
before the process of transcription begins the gene must …… by …….. that move ……
be activated by specific molecules that move from the cytoplasm into the nucleus
What is the name of the compound used in cells to add a phosphate group to a protein?
cAMP
Enzymes can be activated by the addition of a phosphate group.
What is this process called?
phosphorylation
what are the 4 ways of translational control
increasing the speed of breaking down mRNA (if it stays in the cytoplasm it will mean too much protein is made)
activation of initiation factors- help get mRNA into ribosomes
inhibition proteins- stops mRNA getting into ribosomes
protein kinases- phosphorylate the proteins (change their tertiary structure +> function (act as an activator))
what are the specific molecules called that activate the gene before transcription
transcriptional factors
they are proteins
how do transcriptional factors control gene expression? by…
by controlling the rate of transcription
all transcriptional factors contain one or more ….. which
DNA binding domains (DBD’s) which attach to specific sequences of DNA adjacent to the genes that they regulate
what are the 2 classes of transcriptional factors
activators and repressors (inhibitors)
how do activators (transcriptional factors) work, binding
they speed up the rate of transcription as they facilitate the binding of RNA polymerase to the start of the target gene and therefore activate transcription
once bound it activates the specific region of the DNA to commence the transcription process
other mechanisms that TFs use to regulate gene expression
catalyse acetylation or deacetylation of histone proteins
recruit coactivator or corepressor proteins to the tf dna complex
each transcriptional factor …….. and
……… with a ………….. in the DNA molecule
recognises and binds with a specific nucleotide sequence in the DNA molecule
how do repressors (inhibitors) transcriptional factor work
they slow down the rate of transcription by binding themselves to the start of the target gene (operator gene) thereby preventing RNA polymerase from binding- this prevents transcription
what activates transcriptional factors and what does this mean
hormones activate transcriptional factors and thereby stimulate the process of transcription
hormones therefore have the power to activate some genes
examples of products of expressed genes
a polypeptide chain
an enzyme
a tertiary structure of a protein
because they are proteins, gene expression produces a protein
When a gene is transcribed and translated, Biologists say that this
gene is…
gene expression def
expressed
Gene expression is when a gene is transcripted and translated into a proteins.
what is the difference between gene expression and protein synthesis
gene expression refers to the entire process of transcription and translation, protein synthesis refers to the part of translation where aas are assembled into a polypeptide > protein
The process of transcription and translation of a gene is called…
gene expression
how many levels of control of gene expression are there
3
1: control at the transcriptional level
apply transcriptional factors to the production of insulin
bgc is high
activator is released and binds to rna polymerase in the nucleus of a beta cell.
this facilitates binding of rna polymerase to the start of the gene.
the gene for insulin is transcribed and translated.
the gene is then expressed and insulin is produced.
bgc has fallen below the norm
repressor is released inside the nucleus of a beta cell.
rna polymerase cannot bind to the start of the gene.
no transcription and translation of mrna.
gene is not expressed.
insulin is not produced
oestrogens are a group of steroid hormones involved in the oestrous cycle, but they are also involved in …. and how does this happen
dont really need to know all this
gene expression
they control cell growth by affecting the process of transcription
an oestrogen-receptor complex either enhances coactivators or inhibiting corepressors
what is epigenetics
control of gene expression by the modification of dna, all of the different ways gene expression is regulated
study of stable cellular and physiological traits and their underlying mechanisms
eg changes in dna due to environment
the sum of all epigenetic changes in a cell are known as the …
epigenome
cellular mechanisms that respond to the environment but do not alter the dna sequence are classified as …
epigenetic
what are some epigenetic mechanisms (5)
nucleosome positioning, histone acetylation, histone methylation, dna methylation and noncoding rna activity
explain how epigenetic changes might affect the functioning of the genome (3)
methylation of dna base therefore the expression of a gene is changed
if histones are modified this may affect binding of other proteins to dna because dna is wrapped around histones
therefore genes may become activated or repressed
epigenetic changes to dna can cause what types of health issues eg 4
cancer, prenatal changes, brain disorders, chronic diseases
what is a nucleosome
the combination created when dna is wrapped around a histone protein
epigenetics is dependent on the spatial relationship between dna and histone protein
what is histone methylation
the addition of methyl groups makes the histones more hydrophobic so they bind more tightly to each other causing dna to coil more tightly and preventing transcriptions of genes
it is a post translational modification.
usually happens to cytosine
what is histone acetylation/phosphorylation
both reduce the positive charge on the histones making them more negative and so dna (which is negatively charged) coils less tightly, allowing certain genes to be transcribed
because weaker binding makes the dna more accessible to tfs being able to reach it
what are the 2 steps involved in activating a protein by phosphorylation
first cAMP binds to and activated an enzyme called protein kinase
Then, this enzyme phosphorylates the protein
Then, this enzyme phosphorylates the protein.
This changes its tertiary structure
what is an operon
a group of genes that are transcribed at the same time.
they are only found in prokaryotes
usually control an important biochemical process
a cluster of genes under the control of a promoter
suggest why jacob and lwoff would investigate the dna in prokaryotes rather than eukaryotes
it is easier and the dna is free flowing/isnt associated with any proteins and isnt contained in a membrane bound nucleus. in a nucleus you would have to get through the nuclear envelope
there is also the plasmids
what is the lac operon
it contains the genes involved in lactose metabolism
there are 2 regulators that turn the lac operon on and off in response to lactose and glucose levels, what are they
the lac repressor and the catabolite activator protein (CAP)
in what conditions is the lac operon expressed (switched on)
when glucose is low and lactose is present
when is the lac operon not expressed (switched off)
when glucose is high and lactose is non existent
what does the lac repressor act as and what does it do normally and what happens when lactose is present
the lactose sensor
normally it blocks transcription of the operon
when lactose is present it it stops acting as a repressor
senses lactose indirectly through the isomer allolactose (dont need to know)
what does the catabolite activator protein (CAP) act as
what does it activate when glucose levels are LOW
a glucose sensor
activates the transcription of the operon but only when glucose is LOW
it detects glucose indirectly through the presence of cAMP
what are the 3 genes contained in the lac operon
the lacZ, lacY and lacA
what is the role of the lacZ and what is the consequence of what it creates
encodes for latase
which allows lactose to be split into monosaccharides (galactose and b glucose) that can then be fed into glycolysis
what is the role of lacY
it encodes a membrane embedded transporter for lactose so that it can be transported into the bacterial cell to be metabolised
the 3 genes in the lac operon are transcribed as ……. under the control of … ……..
a single mRNA under the control of one promoter
what is the promoter on a lac operon
the binding site for RNA polymerase (enzyme that performs transcription
what is the operator on a lac operon
what happens when the repressor is bound to the operator
it is a negatively charged regulatory site bound by the lac repressor protein
the operator overlaps the promoter. when the repressor is bound SO rna polymerase cannot bind to the promoter and start transcription
what is the CAP binding site
and what happens when cap is bound to the cap binding site
a positively charged regulatory binding site bound by CAP (catabolite activator protein)
when cap is bound to the site it helps rna polymerase bind to the promoter and so promotes transcription
why is glucose a preferred source of energy for prokaryotes eg ecoli
ie why does the lac operon exist
it takes less energy to breakdown as there are less steps so it is easier to breakdown, more favourable
but if glucose is not directly available then the ecoli needs to be able to break lactose down in order to get glucose
describe what happens to the lac operon when lactose is not present
the lac repressor binds tightly to the operator, it blocks RNA polymerase from making its way down the lac operon and so no mRNA is created/no transcription and so there is no translation of lactase
describe what happens on the lac operon when there is lactose
allolactose binds to the lac repressor (so it loses it dna binding ability) and releases it from the operator so RNA polymerase can bind to promoter > transcribe mRNA and lactase can be translated
describe what happens to the lac operon if there is low glucose
cAMP is produced and it attaches to CAP which helps RNA polymerase bind to the promoter resulting in high levels of transcription (mRNA > translation of lactase)
in what conditions is cAMP produced in ecoli
when glucose levels are low
describe what happens to the lac operon when there is high glucose
no cAMP is produced no CAP binds to the cap site so transcription only occurs at a low level
what is morphogenesis
the shaping of an organism by embryological processes of differentiation of cells, tissues and organs and the development of organ systems
what are the 2 types of target dna/dna that is affected by transcriptional factors and what is each of their normal roles
promoters (initiates transcription, long section of dna) and enhancers (stimulate or repress transcription, short section of dna)
what is a homeobox
a dna sequence (around 180 base pairs long) found within hox genes that are involved in the regulation of patterns of anatomical development (morphogenesis)
in animals, fungi, plants and numerous single cell eukaryotes
what are hox genes
a group of related genes that control the BODY PLAN of an embryo along the head-tail axis
they determine the type of structures that will form on a given segment, they confer segmental identity (but do not form the segment themselves)
eg a head in the abdomen region
In animals, a group of homeobox genes control mitosis and apoptosis in the embryonic stag, these genes are called hox genes
what is the protein product of each hox gene called and what is it
a hox protein and it is a transcriptional factor (activate or repress genes)
the same hox protein can repress one …. and …..
gene and stimulate another
the cell cycle and apoptosis are regulated by …… and what can they respond to
hox genes
these genes can respond to internal and external cell stimuli
what is apoptosis
a process that causes cells to die, it removes old cells or cells that are no longer needed
Two cellular processes work together to shape an organism’s body parts.
what are they
mitosis and apoptosis
