Unit 6 - Genetics of living systems Flashcards
Characteristics of genetic code
Universal
Triplet code
Degenerate
Non-overlapping
2 regions of DNA
Introns (non-codingh)
exons (coding)
Introns
charatceristics
Sections of DNA that do not code for a polypeptide
Regulatory sequences
Acts as a buffer for mutations
examples of 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
codes for proteins not used in regulations
Mutagens
give examples
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
what are the levels of control
Transcriptional
Post-transcriptional
Translational
Post-translational
When does up/down regulation occur
what does this do
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
gene
chromosomal
Define Point mutations
what are 3 types
Mutations that occur to a single nucleotide base
Insertion
Substitution
Deletion
what effects can point mutations have on proteins
Silent
Missense (different amino acid coded for)
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 genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the reading frame so the sequence is read diffrently
Silent mutations
A change in the DNA sequence that results in a change to the nucleotide base pairs but has no subsequent effect on on the amino acid produced
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
Benign - No effect on chances of survival
Damaging - 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
Loosley 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
what type of sequence is it
Region of DNA that acts as the binding site for RNA polymerase to start transcription
Intron
Usually upstream
what are operator regions
Short region of DNA, close to the promoter region that along with regulatory proteins control transctription of operons
Downstream
To the right
Upstream
To the left
Operon
group of genes controlled by one promotor and are expressed at the same time
Only found in prokaryotes
How is gene expression regulated in operons
Transcription factors bind to them
Transcription factors
- what codes for them
- what is their function, how do they carry this out
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 or RNA, inhibiting transcription by binding to the operator sequeunce
Gene expression
Production of proteins from a genome
Control of gene expression means what
Whether genes are turned on or off
Why is the control of gene expression necessary
to diffrentiate and specalise cells
Prevent vital resources being wasted
Why is gene expression more complex on eukaryotes
Have to respond to changes in the internal and external environments
DNA wrapped around histones so not exposed = gene expression is harder, prokayoytes dont have these
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
Regulatory site
RNA polymerase is released to stop trancription
what are RNA-coding sequence
Genes that code for 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
How are histones modified
How do the modifications affect DNA packaging
Histones are +vely charged and DNA. -vely charged –> attraction
change to charges change degree of packaging
Acetylation and phosphorylation reduce +ve charge so DNA binds more loosely = transcription happens
Methylation increase +ve charge so transcription doesn’t occur as DNA binds more tightly
How do Transcription factors act as a method of gene expression regulation
- activate or repress RNA polymerase
Methods of gene regulation at the post-transcriptional level
RNA processing
RNA editing
siRNA
what is the process of RNA processing
where does it occur in cell
Pre-mRNA is spliced to remove intrones, mature-mRNA forms
modified nuclotide cap is added at 5’ and adenine tail at 3’ ^Stabilises mRNA and prevents degradation
occur in the nucleus
what is RNA editing
base pair add., deln. or subn in mature-mRNA, which results in different proteins
multiple proteins can be made from one mRNA strand
what are the methos of gene expression regulation 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
