Unit 6 - Genetics of living systems Flashcards
Characteristics of genetic code
Universal
Triplet code
Degenerate
Non-overlapping
Properties of DNA
Introns
Exons
Introns
Sections of DNA that do not code for a polypeptide
Regulatory sequences
Acts as a buffer for mutations
Regulatory sequences
Promoter regions
Terminator regions
Operator regions (prokaryotes)
Exons
Sections of DNA that code for polypeptides
Regulatory or structural genes
Regulatory genes
Genes that code for proteins used in DNA regulation
Structural genes
Genes that code for regular proteins
Mutagens
Chemical, physical, or biological agents which cause mutations e.g. viruses (viral DNA inserts itself into the genome), radiation (Breaks one or both DNA strands)
Where can genes be turned on or off
Transcriptional
Post-transcriptional
Translational
Post-translational
When does up/down regulation occur
Post trasncriptional
Translational
Post translational
Either increases/ decreases rate of protein synthesis
When are proteins modified
Translational
Post translational
Where are ribosomes assembled
Nucleolus
Why is there a ribosomal groove
So mRNA can be read for transcription
Types of mutations
Genes
Chromosomal
Point mutations
Mutations that occur at a spp point
Insertion
Substitution
Deletion
Effects of point mutations of proteins
Silent
Missense
Nonsense
Insertion mutations
Addn. of one or more nucleotide base pairs into a DNA sequence
Substitution mutation
Occurs when a base pair is substituted for another
Deletion mutation
Occurs when a base pair is deleted from the DNA sequence
Frameshift
A mutation caused by the addn. or deln. of a base pair(s) resulting in the translation of the genetic code from an unnatural reading frame from the point mutation to the end of the gene
Silent mutations
Change in the DNA sequence that results to the change in nucleotide base pairs having no subsequent effect on on the amino acid produced
May have occurrred in introns
Missense mutations
A single nucleotide change leads to a different codon and therefore a different AA
Nonsense mutations
Change in nucleotide sequence that leads to one of codons being converted to a terminator codon so the protein produced is truncated
Class of mutations
Beneficial - depends on environment
Neutral - No effect on chances of survival
Disadvantageous - Causes genetic diseases, lessens chances of survival
Histones
Basic proteins that associate w/ DNA in the nucleus and help to condense the DNA into a smaller volume
Little balls in which DNA wraps around
Chromatin
Complex of DNA and proteins that condense to form chromosomes within the nucleus of eukaryotic cells
Euchromatin
Lightly packaged DNA; RNA polymerase can access the bases to transcribe the genes –> genes can be turned on
Heterochromatin
Tightly packaged DNA; RNA polymerase cannot access the bases to transcribe the genes so they are turned off
Promoter regions
Region of DNA that acts as the binding site for RNA polymerase to start transcription
Intron
Usually upstream
Operator regions
Short region of DNA that is close to the promoter region
Interacts w/ regulatory proteins that controls the transcription of operons
Downstream
To the right
Upstream
To the left
Operon
Functioning unit of DNA containing a group of structural genes expressed together
Controlled by one promoter
Only found in prokaryotes
How is gene expression regulated in operons
Transcription factors bind
Transcription factors
Coded for by regulatory genes
Proteins which affects rate of transcription
Activates or inhibits transcription of DNA by binding to promoter region w/ RNA polymerase or blocking the promoter region
Repressor protein
A protein that binds to DNA/RNA inhibiting transcription by binding to the operator
Gene expression
Production of proteins from a genome
Control of gene expression
Whether genes are turned on or off
Why is the control of gene expression necessary
In specialisation and differentiation of cells
Increasing/ decreasing complexity
Prevent vital resources being wasted
Why is gene expression more complex on eukaryotes
Have to respond to changes in the internal and external environments
Histones - DNA not exposed, genes expression is harder
Prokaryotes don’t have histones
Housekeeping genes
Genes that code for proteins which are necessary for reactions in metabolic pathways and are constantly required (enzymes)
Who has only exons
Prokaryotes and eukaryotes without jaw bones
Jaw boned eukaryotes have introns and exons
Terminator region
Does not code for protein
Regulatory site
RNA polymerase is released to stop trancription
RNA-coding sequence
Genes turn into mRNA
Has both introns and exons but introns are removed from premature mRNA during splicing to form mature mRNA
Methods to regulate gene expression at transcriptional level
Histone modification
Transcription factors
Histone modification
Histones are +vely charged and DNA. -vely charged –> attraction
Modify charges to change degree of packaging
Acetylation and phosphorylation reduce +ve charge so transcription happens
Methylation increase +ve charge so transcription doesn’t occur
Transcription factors as a method of gene expression
Control rate of transcription by binding to spp DNA sequences
Regulate genes to make sure they are expressed correctly
Work alone or w/ others as an activator or repressor of RNA polymerase
Regulating gene expression at the post transcriptional level
RNA processing
RNA editing
siRNA
Happens simultaneously
RNA processing
Pre-mRNA is modified –> mature-mRN A binds to ribosme and code for synthesis
Adenine cap is added at 5’ and tail at 3’
Stabilises mRNA and delays degradation in cytoplasm, aids binding
Splicing and the addn. of adenine cap and tail occur in the nucleus
RNA editing
Some mRNA can be changed through base pair add., deln. or subn. Same effects as point mutations and results in synthesis of diff proteins w/ diff function s
Increases range of proteins that can be produced from one mRNA strand
Regulating gene expression at the translational level
Degradation of mRNA
Binding of inhibitory proteins
Protein kinases
Degradation of mRNA
More resilient the molecule, the longer it lasts in cytoplasm, more translation
Binding of inhibitory proteins
Occurs when protein is produced in wrong location or substrate is not available
Regulation of gene expression at the post translational level
Protein activation - allows protein to carry out its function
Protein activation
Occurs in Golgi
Adding non protein groups e.g. carbs, phosphates
Phosphorylation by protein kinases and ATP
Folding/ shortening proteins (2’ structure)
Modification by cAMP
Control sites
Operator region and promoter region
Beta galactoside
An enzyme that catalyses the hydrolysis of lactose to glucose and galactose
Lactose permease
A protein that transports lactose into the cell
Lac i
Regulatory gene
Codes for repressor protein (transcription factor)
Always transcribed
Lac p
Promoter region
Rna polymerase binds here
Lac o
Operator region of control site
Repressor protein binds here
When lactose is present causes a conformational change in repressor protein allowing it to bind to lactose instead
Lac z
Structural gene codes for beta galactoside
Lac y
Structural gene that codes for lactose permease
Lac operon
Inducible operon (only occurs when lactose is present from diffusion through lactose channels )
Example of transcriptional regulation
Group of 3 genes involved in metabolism of lactose
Mechanism of apoptosis
Cytoskeleton broken down by enzymes, loses function
Cell shrinks and the membrane blebs, chromatin condenses
Lysosomes release enzymes which break down cell components
Cell breaks up into membrane-bound fragments
Cell fragments are ingested and digested by phagocytic cells
Uses of apoptosis
Morphogenesis - eliminating excess cells (webbed fingers)
Selection - eliminates non functional cells
Immunity - T killer eliminates dangerous cells (cancer)
Organ size - eliminates excess cells
Tissue remodelling - eliminates cells no longer need (breastfeeding)
Somatic cell
Body cell
Germ line cells
Gametes
Germline mutations
Mutations in gametes so can cause genetic diseases and are passed on
Somatic mutations
Not inherited but can cause ageing and cancer
Result of mutations in normal diploid cells
Homeobox genes
Regulatory genes that contain a homeobox sequence (180 bp)
Highly conserved in animals, plants and fungi
Regulates mitosis and apoptosis in the embryonic stage
Control body plans of an organism
Homeotic genes
Set of genes that control morphology
Homeodomain
Section of the protein coded for by the homeobox sequence (60 AA)
Hox genes
Sub type of homeobox genes
Only found in vertebrates and animals
Found in clusters on chromosomes
Controls body plans and morphology
What do Hox genes code for
A group of TF’s that controls expression of structural genes associated w/ the development of an organism’s appendages during its embryonic stage to form a mature body plan
What does a mutation of a Hox gene lead to
Diff body plan
What ensures features are expressed correctly
Hox genes in a Hox cluster are activated in a particular order depending on where its found on the chromosome
This matches order genes are expressed along H to T
So structural genes are activated in a carefully coordinated sequence
Why are Hox genes highly conserved
V. important
Mutations alter body plans
Mutations are selected against
Polypeptides that control the physical development of an organism
Structural proteins
Enzymes used in metabolic pathways
Hormones
Receptor proteins
Protein kinases
Activated by cyclic AMP and activate proteins through phosphorylation using ATP
siRNA
Small interfering RNA - only needed when cell has made sufficient protein
Complementary base sequence to mRNA that’s to be degraded
Binds to mRNA and activates an enzyme that breaks it down
RNA nucleotides recycled to nucleus
