Chap 19 - Genetics of Living Systems Flashcards
What is a mutation? 19.1
a change in the sequence of bases in DNA
What can happen to protein synthesis if a mutation occurs within a gene? 19.1
it can be disrupted
What is the change in sequence caused by? 19.1
substitution, deletion or insertion of one or more nucleotides within a gene
What is a point mutation? 19.1
if only one nucleotide is affected
What happens when a nucleotide is substituted? 19.1
the codon is changed which could cause it to code for a new amino acid - the primary structure of the protein will be changed
What does the degenerate nature of genetic codes mean? 19.1
the new codon may still code for the same amino acid - no change to the protein synthesised
How does the position and involvement of an amino acid affect during R group interactions? 19.1
the position and involvement of the amino acid in R group interactions determines the impact of the new amino acid on the function of the protein
What is an example of how position and involvement of amino acids impacts a protein? 19.1
if the protein is an enzyme and the amino acid plays an important role within the active site, then the protein may no longer act as a biological catalyst
What happens when nucleotide is inserted or deleted? 19.1
it will lead to a frameshift mutation - the addition/deletion of a nucleotide shifts the reading frame of the sequence of bases (every successive codon from the point of mutation changes)
What is the reading frame of a sequence of bases? 19.1
the sequences of bases are transcribed (read) consecutively in non-overlapping groups of three
What is a triplet code? 19.1
groups of 3 nucleotides that corresponds to one amino acid
When will the reading frame not be changed? 19.1
when the number of nucleotides changed is a multiple of 3 - the final protein formed will still be affected
What happens if there is no effect on the phenotype of an organism? 19.1
normally functioning proteins are still synthesised
What happens if there is damaged caused to a phenotype of an organism? 19.1
it will be affected in a negative way - proteins are no longer synthesised/are non-functional, interfering with essential processes
What happens if a phenotype has a beneficial mutation? 19.1
it is rare for a protein to be synthesised resulting in a new/useful characteristic
What is an example of a beneficial mutation? 19.1
a mutation in the cell surface membrane of human cells means that HIV cannot bind/enter theses cells - means immunity from infection of HIV
What increases the rate of mutations? 19.1
mutagens: chemical, physical or biological agent that causes mutations
What is depurination and depyrimidination? 19.1
depurination - the loss of a purine base
depyriminidination - loss of a pyrimidine base
What can happen during complementary base pairing? 19.1
the absence of a base can lead to the insertion of an incorrect base in DNA replication
What are free radicals? 19.1
oxidising agents
What can free radicals affect? 19.1
they can affect the structures of nucleotides and base pairing in DNA replication
What do antioxidants do? 19.1
known as anticarcinogens due to their ability to negate the effects of free radicals (eg. vitamins A, C and E)
What is an example of a physical mutagen and what does it do? 19.1
ionising radiations (eg. xrays)
- break one or both DNA strands - some can be repaired but mutations can occur in the process
What is an example of a chemical mutagen and what does it do? 19.1
deaminating agents
- chemically alter bases in DNA (eg. converting cytosine to uracil in DNA, changing the base sequence)
What are examples of biological agents and what do they do? 19.1
alkylating agents - methyl/ethyl groups are attached to bases resulting in the incorrect base pairing
bae analogs - incorporated into DNA in place of the usual base during replication, changing the sequence
viruses - viral DNA may insert itself into a genome, changing the base sequence
What is considered a relatively new mutation? 19.1
the ability to digest lactose (sugar present in milk)
What caused lactose intolerance? 19.1
when majority of mammals ceased to suckle - found primarily in European populations who are more likely to farm cattle
What benefits does lactose tolerance have in adults? 19.1
prevents diseases such as osteoporosis - could have prevented individuals from starving during famines
What differences are there between gene mutations and chromosome mutations? 19.1
- chromosome mutations affect the whole chromosome or a number chromosomes within a cell
- gene mutations occur in single genes or sections of DNA
Describe deletion as a change in chromosome structure 19.1
section of chromosome breaks off and is lost within the cell
Describe duplication as a change in chromosome structure 19.1
sections get duplicated on a chromosome
Describe translocation as a change in chromosome structure 19.1
a section of one chromosome breaks off, is reversed and then joins back onto the chromosome
Describe inversion as a change in chromosome structure 19.1
a section of chromosome breaks off, is reversed, then joins back onto the chromosome
What is a silent mutation? 19.1
they do not change any proteins or the activity of proteins synthesised - no effect on phenotype of an organism - may result in change to primary structure but do not change overall structure
Where do silent mutations occur? 19.1
in non-coding regions of DNA (introns) or code for the same amino acid due to degenerate code
What is a nonsense mutation? 19.1
result in codon becoming a stop codon
What is the result of a nonsense mutation? 19.1
result is shortened protein being synthesised which is normally non-functionally - normally have negative/harmful effects on phenotypes
What is a missense mutation? 19.1
result in the incorportation of an incorrect amino acid into primary structure when protein is synthesised
What do missense mutations depend on? 19.1
the role the amino acid plays in the structure and function of protein synthesised - could be silent, beneficial or harmful
When do conservative mutations occur? 19.1
when the amino acid change leads to an amino acid being coded for which has similar properties to the original - the effects of mutation are less severe
When do non-conservative mutations occur? 19.1
when the new amino acid has different properties to the original - more likely to have an effect on protein structure (may cause disease)
What are housekeeping genes? 19.2
the genes that code for enzymes necessary for reactions present in metabolic pathways (eg. respiration)
What are protein-based hormones required for? 19.2
growth and development of an organism or enzyme - only required by certain cells at certain times to carry out a short-lived response - coded for by tissue-specific genes
Where are entire genomes present? 19.2
in every prokaryotic cell or eukaryotic cell containing a nucleus - includes genes not required by that cell so the expression of genes and the rate of synthesis of protein products
What can genes do as demand changes? 19.2
turn off - or the rate of product synthesis can increase/decrease
Why are bacteria able to respond to changes in environment? 19.2
due to gene regulation - genes expressed only when products are needed prevents vital resources being wasted
Why is gene regulation different in eukaryotes? 19.2
the stimuli that cause changes in gene expression and the responses produced is more complex - multicellular organisms have to respond to change in external environment but also internal environment
Why is gene regulation required? 19.2
for cells to specialise and work in a coordinated way
What 4 ways can genes be regulated? 19.2
- transcriptional: genes can be turned on/off
- post-transcriptional: mRNA can be modified which regulations translation and types of proteins produced
- translational: translation can be stopped/started
- post-translational: proteins can be modified after synthesis which changes their functions
What happens to DNA in orderfor it to pack into the nucleus? 19.2
as DNA is very long, it has to be wound around proteins (histones) - resulting complex is chromatin
What is heterochromatin? 19.2
tightly wound DNA causing chromosomes to be visible during cell division
What is eurchromatin? 19.2
loosely wound DNA present during interphase
When is transcription of genes not possible? 19.2
when DNA is tightly wound - RNA polymerase cannot access the genes
Why does protein synthesis happen during interphase? 19.2
ensures proteins necessary for cell division are synthesised in time + prevents complex, energy-consuming process of protein synthesis from occuring when cells are actually dividing
Why does DNA coil around histones? 19.2
they are positively charged (DNA is negatively charged) - histones can be modified to increase/decrease degree of packing (or condensation)
What causes DNA to coil less tightly and allow certain genes to be transcribed? 19.1
the addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces positive charge on the histones (making them more negative)
What causes DNA to coil more tightly and prevent transcription of genes? 19.2
the addition of methyl groups (methylation) makes histones more hydrophobic - they bind more tightly to each other
Define epigenetics? 19.2
describe the control of gene expression by modification of DNA - sometimes used to include all all the different ways in which gene expression is regulated
What is an operon? 19.2
a group of genes that are under the controll of the same regulatory mechanism and are expressed at the same time
Why are prokaryotic genome structures smaller and simpler? 19.2
operons are more common in prokaryotes
Why are operons an efficient way to save resources? 19.2
if certain gene products aren’t needed, all genes involved in their production can be switched off
What happens if glucose is in short supply? 19.2
lactose can be used as a respiatory substrate
Why is glucose the preferred substrate of Escherichia coli (and other bacteria)? 19.2
it is easier to metabolise
What is a lac operon? 19.2
a group of 3 genes, lacZ, lacY and lacA involved in metabolism of lactose - structural genes (code for three enzymes and are transcribed onto a single long molecule of mRNA
What 3 enzymes are coded for by lac operons? 19.2
beta-galactosidase, lactose permease and transacetylase
Describe the role of the regulatory gene, lacI 19.2
it is located near the operon - codes for repressor proteins that prevents transcription of structural genes in the absense of lactose
Where does the repressor protein bind to? 19.2
an area called the operator - close to structural genes
What does the binding of the repressor protein prevent? 19.2
prevents RNA polymerase binding to DNA and beginning transcription - known as down regulation
What is the promoter? 19.2
the section of DNA that is the binding site for RNA polymerase
How are enzymes synthesised when lactose is present? 19.2
lactose binds to repression protein causing it to change shape so it can’t bind to operator - RNA polymerase can bind to the promoter, the three structural genes are transcribed and enzymes are synthesised
How is the required quantity of enzymes produced to efficiently metabolise lactose? 19.2
binding of RNA polymerase results in relatively slow rate of transcription that can be increased/up-regulated
How is this achieved? 19.2
the binding of cAMp reception protein (CRP) - only possible when CRP is bound to cAMP (a secondary messenger)
What happens as glucose is transported into an E. coli cell? 19.2
cAMP levels decrease, reducing transcription of genes responsible for metabolism of lactose
What happens if both lactose and glucose are present? 19.2
the preferred respiratory substrate, glucose, is metabolised
What is pre-mRNA? 19.2
the precursor molecule produced in transcription
What happens to pre-mRNA? 19.2
it is modified to mature mRNA before binding to ribosome to code for synthesis of required protein
What are caps and tails, what do they do? 19.2
caps are added to 5’ end (modified nucleotide), tails are added to 3’ end (long chain of adenine)
- help stabilise mRNA and delay degradation in cytoplasm
- caps also add binding of mRNA to ribosomes
What is splicing? 19.2
where RNA is cut at specific points - introns (non-coding DNA) are removed and exons (coding DNA) are joined together
What happens in RNA editing? 19.2
nucleotide sequence of mRNA molecules can be changed by addition, deletion or substitution - similar effect to point mutations and result in synthesis of different proteins (may have different functions)
What is the result of RNA editing? 19.2
the range of proteins produced from a single mRNA molecule or gene increases
Describe how degradation of mRNA regulates the process of protein synthesis 19.2
the more resistant the molecule, the longer it will last in the cytoplasm - a greater quantity of protein synthesised
Describe how the binding of inhibitory proteins regulates protein synthesis 19.2
binding of inhibitory proteins to mRNA prevents it binding to ribosomes and synthesis of proteins
Describe how activation of initiation factors regulate protein synthesis 19.2
aids the binding of mRNA to ribosomes - eggs of many organisms produce large quantities of mRNA which is not required until after fertilisation when initiation factors activate
What are protein kinases? 19.2
enzymes that catalyse the addition of phosphate groups to proteins
What does the addition of a phosphate group do? 19.2
changes the tertiary structure and therefore function of the protein
What are protein kinases important regulators of cell activity? 19.2
many enzymes are activated by phosphorylation
What are protein kinases activated by? 19.2
by the secondary messenger cAMP
What does post-translational control involve? 19.2
modifications to proteins that have been synthesised
What controls the growth & development of most life forms? 19.3
the same small group of genes
What is morphogenisis? 19.3
the regulation of the pattern of anatomical development
How were the genes discovered? 19.3
scientists investigated strange mutations in fruit flies - legs on head, extra wings
Why are fruit flies (Drosophola) a popular choice for genetic studies? 19.3
small, easy to keep and short life cycle
What are homeobox genes? 19.3
group of genes that contain a homeobox
What is a homeobox? 19.3
sectin of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is similar in plants, animals and fungi
each amino acid contains 3 bases (60x3=180)
What is a homeodomain? 19.3
the part of the protein that binds to DNA and switches other genes on/off
Why do homeobox genes in mice and humans have identical nucleotide sequences? 19.3
accumulated mutations and evolution from a common ancestor (approx. 60 million years ago)
What is Pax6? 19.3
a homeobox gene
What happens when Pax6 is mutated? 19.3
causes a form of blindness (due to underdevelopment of retina) in humans, mice and fruit flies
What has been found about the Pax6 gene? 19.3
it is a gene involved in development of eyes in humans mice and fruit flies
What are the 3 types of body symmetry in animals? 19.3
- radial: seen in diploblastic animals (eg. jellyfish) - no left or right, just top and bottom
- bilateral: both left and right sides, head and tail
- asymmetry: seen in sponges - no lines of symmetry
What is the role of apoptosis in genetics? 19.3
- shapes different body parts - removing unwanted cells and tissues
- release chemical signals to stimulate mitosis and proliferation - leads to remodelling of tissues
(compared to a sculptor shaping a block of wood/stone)
What is the role of mitosis in genetics? 19.3
increase number of cells leading to growth
What regulates mitosis and apoptosis? 19.3
hox genes
What are hox genes? 19.3
one group of homeobox genes only present in animals
term is often interchanged with homeobox genes
What are hox genes responsible for? 19.3
correct positioning of body parts
How are hox genes found in animals? 19.3
in gene clusters - mammals have 4 clusters on different chromosomes
The order in which genes appear along the chromosome is..? 19.3
the order in which their effects are expressed in the organism
How many hox genes do humans have? 19.3
39 - believed to have arisen from one ancient homeobox gene by duplication and accumulated mutations
How are body plans represented? 19.3
as cross-sections through the organism - showing funamental arrangement of tissue layers
How many tissue layers do diploblastic and triploblastic animals have? 19.3
diploblastic: 2
triploblastic: 3
What is a common feature of animals? 19.3
segmentation - eg. rings of a worm, back bone vertebrates
What do different hox genes control? 19.3
- hox genes in head: development of mouthparts
- hox genes in thorax: development of wings, limbs, ribs
How are vertebrae and associated structures developed? 19.3
from segments in the embryo - somites
How are hox genes involved with somites? 19.3
somites are directed by hox genes to develop in a particular way depending on position in sequence
What can expression of regulatory genes be influenced by? 19.3
internal + external environment
What is stress in genetics? 19.3
condition produced when homeostatic balance within an organism is upset - due to change in temp/light intensity
What causes internal changes in genetics? 19.3
release of hormones/psychological stress
