Genetics Flashcards
Phenotype:
Discernible properties of an individual.
Genotype:
The genetic information that influences discernible properties.
What are the two types unicellular eukaryotic organisms?
Fungi and Protoctista
What makes up eukaryotic chromosomes?
Chromatin (DNA and Histone proteins)
What is cytogenetics?
The study of chromosomes.
What is the karyotype?
The chromosome complement of an individual.
What is the p arm of a chromosome?
The “petite” (shorter) arm
What is the name of the longer arm of the chromosome?
The q arm
How many chromosomes in a healthy human are autosomes?
22
What is meant by diploid?
Two homologous chromosomes with the same genes but different alleles.
Are all eukaryotes diploid?
No.
What is a gene?
A unit of hereditary information that occupies a fixed position on a chromosome.
What are the 3 regions which typically make-up a eukaryotic protein-coding region?
The upstream flanking region, the transcriptional unit, the downstream flanking region.
Cytoplasmic inheritance?
Some DNA in mitochondria and chloroplasts. Organelles originate from ancient endosymbiotic events. As egg cell has large volume, cytoplasmic inheritance is determined by maternal inheritance.
Euchromatin:
Loosely packed chromatin.
Heterochromatin:
Condensed structure that does not allow the expression of genes in that region.
Why is there variation between cells of multicellular organism?
Specialisation (differentiation) can occur post division -> share genetic information, however differ in expression.
Why is eukaryotic DNA replication “semi” continuous?
The 5’ to 3’ leading strand is replicated continuously, whereas the 3’ to 5’ lagging strand is replicated in fragments.
G1: Cell cycle
Cell increases in size, ribosomes and RNA produced, DNA prepared for synthesis.
S phase: Cell Cycle
DNA is synthesised.
G2 Phase: Cell Cycle
Cell check for fidelity of the DNA, prepares for nuclear division.
Prophase:
Chromosomes condense -> become visible. Chromosome now comprises 2 chromatids and a single centromere.
What protein holds together sister chromatids?
Cohesin
The mitotic spindle:
Cytoskeletal structure made of microtubules (tubulin protein polymer). The spindle separates sister chromatids to daughter cells -. achieves this by shortening microtubules.
Centromeres:
Specialised region of the chromosome that direct the equal segregation of chromosomes during mitosis. Defined by specific epigenetic markers. Can be found at any point along the chromosome. Connect to microtubules by kinetochore.
Kinetochore:
Large protein complex connecting centromere to microtubules (mitotic spindle)
Metaphase:
Centromeres align at the spindle equator. Microtubules attaching to each pole cause tension holding chromosomes in place.
Anaphase:
Sister chromatid cohesion breaks down. Chromatids separates forming chromosomes. Centromeres start moving to opposite poles.
Telophase:
Chromosomes arrive at cell poles -> decondense -> nuclei form
Cytokinesis:
Division of the cell, formation of a “cleavage furrow” between poles as protein ring contacts.
Function of meiosis?
Halves the chromosome number in cells through two successive nuclear divisions.
Nuclear cycle in Saccharomyces cerevisiae:
Haploid throughout most of life cycle -> a and alpha mating types -> a and alpha combine to form diploid -> meiosis occurs -> 4 haploid products.
Meiosis 1:
Daughter cells produced have chromosomes containing chromatids of one chromosome from each pair.
What are the 5 stages of meiosis 1:
Leptotene, zygotene, pachytene, diplotene, diakinesis
Leptotene:
1st stage of meiosis 1: Replicated chromosomes contract
Zygotene:
2nd stage of meiosis 1: Chromosomes line up in homologous pairs, form synapsis. Homologous pair held together by synaptonemal complex.
Pachytene:
3rd stage of meiosis 1:
Crossing over between non-sister chromatids + genetic exchange.
Diplotene:
4th stage of meiosis 1: Chromosomes separate a bit but sites of crossing over are still visible
Diakinesis:
5th stage of meiosis 1: Chromosomes contract further -> less crossing over.
How does meiosis generate variation through independent assortment:
Orientation of bivalents on meiosis spindle is random, and the combination of inherited chromosomes in the daughter cells is random.
What is a wild type allele?
The form that predominates in nature -> makes up laboratory stock.
What types of mutation are inheritable?
Mutations in gametes
What is the effect of spontaneous mutation in meiosis?
Increased variation in progeny.
what are the 3 types of polyploidy?
Triploidy, Tertraploidy, Monoploidy
What is polyploidy?
An unusual number of chromosome sets.
What is the normal number of chromosome sets in a human?
2n
What is Aneuploidy:
One or a few individual chromosomes are extra/missing.
Sources of mutation:
Mistakes during replication (Point mutations and small insertions/deletions), Transposons, Incorrect repair of DNA,
What is a null allele:
An allele where mutation has led to complete loss of function.
What are types of point mutations?
Silent, nonsense, and missense,
What are auxotrophic mutants?
Mutants that are unable to synthesise essential compounds.
What type of auxotrophic must occur for an organisms to still be able to survive?
A non-allelic auxotrophic mutations.
Pure breeding lines:
All offspring from matings within the line have the same character (phenotypes)
Chi-square equation:
Chi^2 = sum of ( (observed - expected)^2 / expected)
Degrees of freedom:
The number of parameters that can vary independently.
What is the degree of freedom for a chi^2 test?
Number of classes - 1.
What are viruses?
Genetic elements that cannot replicate independent of a living host cell -> can exist as particles outside host.
Why does the size of viruses impact their ability to replicate?
Viruses can only carry small volume of genetic material -> doesn’t have sequences req. for independent replication.
Range of viral genome size:
0.5-1000kb (kilo bases)
They can have fewer than 5 genes.
What is virion?
The extracellular form of the viral nucleic acid surrounded by protein.
Assembly of virion: How does it reduce the need for structural genes?
Small number of protein species make up the capsid-> these don’t require as many structural genes due to self-assmebly
What ensures the transcription of viral genes over host genes upon infection?
T4 lysozomes.
Function of early proteins synthesised by viruses?
They’re involved in the replication of the DNA and to synthesise copies.
Sigma factors:
Aids transcription via RNA polymerase by providing specificity to bind to promoter region.
How do viruses trick host cells into transcribing viral rna?
Viral sigma factors lead to RNA polymerase binding to the viral genetic information.
How do viruses prevent host transcription?
The phage encodes for anti-sigma factors -> binding to host sigma factors and prevent transcription.
How are middle proteins synthesised in viral infections?
early proteins bind to host RNA polymerase and alter the alpha subunits to recognise middle protein promoters.
What’s significant about the sequential order of protein synthesis during viral infection?
Allows for the guiding of structures to synthesise middle mRNA and middle proteins to then transcribe late proteins.
Lysogeny:
Stable genetic relationship between virus and host.
Temperate bacteriophages:
Phages which have the capacity to integrate their genetic information.
Steps of initial viral infection:
Attachment -> injection of DNA/RNA -> lytic or lysogenic pathway.
Lytic lifecycle:
Viral DNA replication -> protein synthesis -> assembly -> lysis
Lysogenic Pathway:
Viral DNA integrates into Host DNA (sometimes into host chromosome and forms prophage) -> remains through cell division and replicates in synchrony with the host cell DNA.
What is induction (viral infection)?
The process of swapping from the lysogenic pathways into the lytic pathway and form virions.
What are repressors?
Proteins that switch off the lytic pathway
Induction requires what?
the inactivation of repressors or the prevention of their synthesis.
AttLambda:
The attachment site at which the viral genome integrates -> requires enzyme Lambda integrase.
What type of enzymes are integrases:
Ligases.
How is phage DNA replicated?
The “rolling circle mechanism”
“rolling circle mechanism”
DNA is continuously synthesised into concatemer using an unbroken template strand -> synthesised it acts as a secondary template for primers to attach to -> allowing for the replication of complimentary template strand -> after complete copy of genome finished -> cut and separated.
What do many animal viruses have around their coat?
A membrane to allow them to enter the host cell via endocytosis.
How do animal viruses replicate their DNA?
They integrate into host Chromosome and are transcribed.
What kind of genetic information do Animal viruses carry?
RNA or DNA based genomes.
What feature of eukaryotic cell mRNA acts as a barrier to viruses?
mRNA is processed before translation -> therefore the viral mRNA will not have the correct cap/markers to be translated.
Name the protein cage surrounding DNA:
The Capsid
Polyprotein method eukaryotic viruses:
ssRNA made to look like spliced mRNA (has a 3’ tail and 5’ VPG cap) -> allows for the ssRNA to be translated -> form viral proteins.
How do RNA viruses inhibit the action of host RNA?
They use enzymes to destroy the cap binding proteins within the host cell.
Rabies:
Uses viral RNA replicase -> used to increase RNA amount in host cell -> increase freq. of translation. -ve parental RNA strand is transcribed vRNA polymerase into mRNA (+ sense) -> translated using host enzymes. -> increased synthesis of + strand RNA.
Influenza:
-ve strand RNA genome strand is segmented. Neuraminidase to breakdown sugar coat on host cell envelope.
Complex structure with many accessory proteins. Has 8 linear ssRNA molecules.
Hemagglutinin - binds to receptors and triggers fusion of membranes.
Influenza: Replication
-Takes place within host nucleus.
-Overall pattern of genomic RNA synthesis -> resembles rabies pathway.
-viral mRNA synthesised given 5’ caps (cut from primers) and PolyA tails
What is Antigenic shift?
Portions of the RNA genome from 2 genetically distinct strains, both infecting a cell are reassorted -> leads to different surface proteins.
HIV:
-Retrovirus.
-2 strands of ssRNA
-Genome is replicated through a DNA intermediate.
-viral reverse transcriptase is used for replication.
What are the three regions of HIV’s genome?
gag, pol, and env
HIV: gag
Encodes structural proteins
HIV: pol
encodes reverse transcriptase and integrase
HIV: env
Encodes envelope proteins.
HIV: Replication pathway
Entrance -> uncoating -> ssRNA is reverse transcribed -> travels into the nuclease and integrates into host DNA -> transcribed in mRNA -> encapsidation -> budding -> release
HIV: gene expression
As a provirus the viral genome can be latent. Promoters activated in the LTR region -> leads to mRNA transcripts being capped and polyadenylated.
DNA viruses of eukaryotes:
Mainly polyomaviruses (replicate in host nucleus + can induce tumours) and pox viruses
SV40:
Polyoma virus
-Genome is double stranded DNA circle
-Used as a vector for moving genes into eukaryotes
-No-viral encoded proteins
-Has overlapping genes to allow for more proteins to be synthesised -> compensate for small genome size.
Corona Virus:
-Single +ve strand of RNA
-Replicates in cytoplasm.
-Respiratory infection
-Glycoprotein “crown” on caspid -> aid attachment to host membrane
Corona Virus: Infection Cycle
5’ cap and Poly A tail on viral mRNA -> replicase translated -> -ve generated -> transcribes either monocistronic mRNAs (translated for v. proteins) or genome copies.
Length of E.coli DNA:
1mm
Genomic decay:
The removal of unnecessary coding regions of the genome.
What is an operon?
DNA sequence responsible for the organisation of a single gene and surrounding regions
Myxo bacteria:
Have much larger genomes than ordinary bacteria and-so can have much more complex lifestyles.
What are regulons?
Large networks of operons involved in coordinating physiological responses. These are controlled by regulatory proteins.
Nucleoid:
Structure in prokaryotes where DNA loops are bound to histone-like proteins.
Planktonic meaning:
Bacteria can freely swim
Sessile meaning:
Bacteria are in fixed place and unbale to move.
What form is DNA stored as in prokaryotes?
+ve or -ve supercoiled.
Topoisomerases:
Prokaryotic:
Make a double-stranded break in the DNA circle -> insert DNA into the break -> reseals the break
Prokaryote DNA replication:
Replication starts at origin -> “bubble” forms and forks progress in opposite directions. -> one strand continuously and the other discontinuously -> replication ends at the terminus.
How do prokaryotes use promoters to control gene expression?
They have a mixture of promoter regions with different specificities to RNA polymerases. Strong promoters synthesise more protein.
Redundancy:
Successful normal functioning can occur despite physiological changes and changes to the genome.
What structure is formed following the DNA replication of prokaryotes:
catenane ring (Looks like key ring)
K-12:
E.coli strain
Circular genome (4288 genes or more)
Transcription occurs either Clock wise or anti-CW.
What can be used to identify a DNA sequence?
Extra genomic DNA.
PBR322:
-Common plasmid used for cloning.
-Two anti-biotic resistance genes (selectable marker)
-Named restriction sites
Rolling circle model Plasmid replication:
Similar to rolling circle for viral genome -> works one strand at a time, once first is replicated it’s displaced and will bind to complementary strand once replication is finished.
Plasmid-conferred phenotypes:
Antibiotic production, conjugation, metabolic function, resistance to toxins and antibiotics
Properties of prokaryotic mutations:
Heritable, rare, good, bad, or neutral, usually “small”
Purpose of gas vesicles in bacteria:
Gas vesicles surrounded by hydrophobic membranes can be used to control the buoyancy of the cell.
Difference between screening and selecting:
Selecting -> find a primary property.
Screening -> find properties we want/desire (e.g nutritional deficiency)
What is nomenclature differentiates a wild type gene from a mutant gene?
A plus(+) in superscript
What in nomenclature is used to differentiate between the presence or absence of a property?
Plus or Minus in superscript
What case letters should be used to write phenotype nomenclature?
All capitals
What agents can cause mutations?
Base analogs, Chemicals, Intercalating dyes, and Radiation.
Prokaryote Transformation:
The uptake of naked DNA from a lysed cell. (In the environment)
Prokaryote Transduction:
Recipient bacteria uptakes DNA from a bacteriophage, carrying donor DNA.
Prokaryote Conjunction:
The donor and recipient cell transfer genetic information across pilus
Mechanism of Transformation:
-Naked DNA binds via protein to surface membrane ->one strand enters via DNA translocase -> binds to RecA -> RecA-ssDNA complex stretches to dsDNA -> Branch migration and homologous recombination occurs
Mechanism of Transduction:
Phage containing host DNA post lytic cycle inserts DNA into acceptor and the DNA integrates via homologous recombination.
Mechanism of Conjunction:
The structure used to transfer this information is a pilus. This takes place during the process of cell “mating”/pairing. The pilus is depolarised near the acceptor cell, sub units of the pilus are disassembled leading to a contraction.
What is a fertility plasmid?
A plasmid that is required to donate plasmid DNA and genetic information to other cells.
What triggers the disassemblement and contraction of the pilus?
The depolarisation of the pilus near the acceptor cell.
What two processes work against each-other during transformation?
Degradation of DNA + protection of the DNA by RecA.
What are Hfr strains?
High frequency of recombination strain -> has an integrated F plasmid within the chromosome allowing for integration of chromosomal genes into an acceptor.
What are Hfr strains used for?
The integration of chromosomal genes via an F plasmid.
Transformation use in laboratory:
Get plasmid or fragments of linearised DNA into numerous bacterial cell type. This can be done naturally or vita chemical treatment or electroporation.
Transduction use in laboratory:
Used to move small fragments of DNA, gene or transposon from one cell to another.
Conjunction use in laboratory:
Useful historically - not much use now.
Conjunction use in laboratory:
Useful historically - not much use now.
How were Hfr’s used to identify the genome sequence of E.coli?
Different Hfr strains can be used will integrate in different orientations. -> positions of the Hfr genes can be tracked at different points to track the time it takes for complete transfer.
When are chromosomal disorders identified?
Prenatal or live birth
How many live births display chromosomal abnormality?
0.1% -> aneuploidy
Term for when all mtDNA in a cell is the same:
Homoplasmic
Term for when mtDNA in a cell is the differs due to mutation:
Heteroplasmic
How are mitochondrial disorders inherited?
Maternally -> the cytoplasm of the egg cell.
Single Gene disorders:
-Disease alleles at a single gene
-Follow mendelian inheritance
-Individually rare, collectively common
-High penetrance
-Tests are predictive
Complex Disorders:
-Risk alleles are at multiple genes (polygenic)
-No simple inheritance patterns (although there is a genetic component)
-Mutations suggest susceptibility to disease.
-No reliable tests
-Influenced by environment
Introns:
Non-coding regions of DNA
Exons:
Coding-regions of DNA
Non-coding region function (intron):
Contains regulatory elements and promoters to allow for the transcription of coding regions.
ENCODE project:
Aims to form an encyclopaedia of DNA Elements within the human genome.
Autosomal Diseases:
-1 copy of mutation is sufficient for the individual to be affected.
-Wild type is recessive, mutation dominant
Huntington’s Disease:
-Late onset - 1 in 10,000
-Dominant autosomal disease.
-Progressive neurodegenerative disease
-Neuronal death, cerebral atrophy, CNS disorder, uncontrolled movements, decrease in cognitive function
- Caused by htt gene
What causes Huntington’s Disease:
-Polyglutamine repeats -> will have more than the normal 36 copies of CAG. -> At the number of CAG repeats -> onset is earlier (genetic anticipation)
-Poly Q expansion leads to misfolding and aggregation in neuronal bodies -> leads to symptoms.
Cystic fibrosis:
-1 in 2000 affected, 1 in 22 carriers
-recessive autosomal
-Build-up of mucous that damages organs
-cftR gene and mutation responsible
What are the therapies used to treat cystic fibrosis?
-Physiotherapy
-DNAase to reduce mucous viscosity
-Anti-biotics and anti-inflammatories
-Mannitol spray -> increase osmolarity of mucous
What is the function of CFTR protein (cystic fibrosis):
Transports Cl- ions across the plasma membrane of the cell that line the lungs -> ensures the hydration of the airways surface layer.
What type of mutations can lead to cystic fibrosis?
Mis-sense, nonsense mutations -> cause by point mutations
or frame shifts
What is cystic fibrosis treatment specific to?
The type of mutations present in the CFTR gene.
How are class 1 mutations in CFTR treated?
-Production correctors to promote transcription
-Treats nonsense mutations.
How are class 2 mutations in CFTR treated?
-Correctors (lumacaftor)
-Improve the intracellular processing of CFTR
-(e.g delta Phe508)
How are class 3 + 4 mutations in CFTR treated?
-Potentiators (Ivacaftor)
-Recovers the function of CFTR
-Treats missense (e.g treats G551D and R117H)
X-linked disorders?
Genes located on X chromosome -> mostly recessive -> males can inherit from female carrier parent -> females can from a carrier mother and affected father.
Duchenne Muscular Dystrophy:
Early onset - 20-30years life exp.
-Passed by mother
-multi-system disorder causing muscle weakness, wasting and atrophy.
-mutations in Dystrophin protein
Two types of Duchenne Muscular Dystrophy:
-Deletion of one exon -> (Between 40-54) -> causes frame shift -> loss of function (early stop codon or large missense)
-In frame mutation without shift -> far less severe (small missense)
Treatment for Duchenne Muscular Dystrophy:
Anti-sense Oligonucleotide treatment: Blocks exon containing premature stop codon -> greater length protein -> increases function.
-Eleplisen (drug used)
Threshold hypothesis of disease:
Polygenes and environment lead to a distribution of liability. Once liability exceeds a threshold the disease occurs.
Why do polygenic diseases show a continuous phenotype?
Many loci contribute to the variation -> leading to a range of phenotypic variation.
What are diff. architectures of complex diseases:
-Small number dominant alleles confer large increase in risk.
-Many alleles confer small increase risk
-One major allele exerts large effect on numerous low risk factor alleles.
Single Nucleotide Polymorphisms:
-Uneven distribution in genome
-Occur at coding regions: synonymous + non-synonymous
-Or occur at non-coding regions
What is a synchronous SNP?
A single nucleotide polymorphism (point mutation) results in no change to encoded aminoacid
Effect of SNP’s at non-coding regions:
Affects expression/regulation of associated genes -> leads to complex diseases -> caused by many SNPs
Exome Aggregation Consortium:
Exomes from unregulated individuals are sequenced as part of various-disease specific and population studies -> 7million variants -> records freq. of diseases and documents rare mutations
-Highly pathogenic variants less common
What is the exome?
The sequence of all exons within the genome.
Genome Wide Association Studies: Issues
-requires many participants-Examine panel of SNPs for association with disease
-Missing loci contribute to “missing heritability” -> leading to a known genetic component not being identified.
-Gwas
Genomic Wide Association Studies:
-Compare allelic freq. across the entire genome in a case and control population.
-Significant diff. in allelic freq. between case and control population = association with disease.
Linkage Disequilibrium:
The non-random association of alleles at different genomic loci
What does linkage disequilibrium depend on?
Distance between alleles + recombination rate
What can be used to model and analyse linkage disequilibrium?
Haplotype blocks -> each block represent SNP assosciated with disease.
What is the odds ratio?
Stat that quantifies the strength of association -> used to measure strength of associations between SNP and diseases
What can be determined if the odds ratio = 1:
the events are independent
What can be determined if the odds ratio > 1:
The events are correlated (there is an association)
What can be determined if the odds ratio < 1:
The events are weakly associated
What is the p value accepted for a GWAS value to be significant:
p < 5x10^-8
What can be used to identify risk variant SNPs?
Manhattan plot or GWAS studies (Have a high rate of false negatives)
Type 2 diabetes:
-Common chronic conditions -> caused by inability to take up sugar
-Characterised by high blood sugar
-Diabetes is a multifactorial disease.
What are the environmental factors that are associated with an increased risk factor for type 2 diabetes:
Familial, Geography, ethnicity, age, weight, diet, and level of physical activity.
What genes are associated with type 2 diabetes?
TCF7L2 -> allele providing the greatest risk of type 2 diabetes -> intronic variant -> codes for transcription factor for pancreatic development, FTO -> intronic variant -> regulates body weight, and CDKN2A/B -> non-coding regulatory variant
Breast Cancer:
Heritable risk
Rare Coding mutations + common non-coding variants increase risk.
How were BRCA1 and BRCA2 mapped?
linkage analysis
What are the rare coding mutations which greatly increase the risk of breast cancer?
BRCA 1, BRCA 2
What can cause missing heritability?
-False negative
-Rare variant alleles
-Structural alteration of the genome
-Epigenetics
-3D genome organisation
Proteome:
The set of proteins synthesised by a cell.
Haematopoiesis:
A hematopoietic stem cell gives rise to different blood cells.
What occurs when a stem cell divides?
A new stem cell is produced and a second progenitor cell -> which generates new lineages.
What is significant about the generation of stem cells during stem cell division?
Self-renewal prevents the depletion of stem cells.
Totipotent:
Can form a whole new organism
Pluripotent:
Can form many cell types but not all
Multipotent:
Can form fewer cell types than other stem cell types.
Where are embryonic stem cells taken from?
Inner cell mass from a blastocyst -> under tissue culture conditions.
Uses of embryonic stem cells:
Introduce genes, knockout genes (reverse genetics), Manipulate chromosome (rearrangements/deletions), Make specific genome edits (sequence level)
How can a chimeric organism be produced?
Inject modified ESC cells into a blastocyst -> Implant this into a pseudopregnant mouse. Cells in the mouse will have derived from two genotypes.
How many genotypes does a chimeric organism have?
2 simultaneously.
How much of the genome codes for proteins?
1%
How many pairs of chromosomes doe Drosophila melanogaster have?
4 pairs, XY,2,3,4
How many genes in Drosophila melanogaster:
16,000 genes
What genes regulate an organisms body plan?
Hox genes
What kind of mutations result in disfigured phenotypes:
Recessive autosomal mutations in the hox genes.
What differentiates the body plans of closely related animals?
The complement of hox genes
The two categories of genes regulating segmentation pattern:
Maternal Effect Genes + Zygotic Genes
Zygotic Genes: 2 types
Segmentation genes - regulate feature of segments
Homeotic genes - determine structures found on segments.
Zygotic genes:
The phenotype of the individual is dependent on the individual’s genotype.
Maternal Effect Genes:
Maternal genotype can determine the phenotype of progeny was therefore developed.
Which genes are responsible for the earliest stages of development?
Maternal Effect Genes.
Effect of mutations in maternal genes on larvae:
Can lead to deletions of particular regions of the embryo.
Where are BICOID and NANOS mRNA and proteins located in larvae/embryo?
At the anterior and posterior poles.
What is a key in the control of the expression of zygotic genes:
The conc. of BICOID and NANOS mRNA and proteins.
What are BICOID and NANOS?
Maternal effect genes.
What are the 3 categories of zygotic genes that determine the identity of domains in the embyro?
GAP genes, Pair-rule genes, and Segment Polarity Genes.
Homeotic mutation phenotypes:
regions or segments aren’t deleted but are instead replaced by another organ/segment,
Homeotic mutation phenotypes:
regions or segments aren’t deleted but are instead replaced by another organ/segment,
Gene expression of Bacteria: transcription initiation
-The RNA polymerase (a2bb’sw) scans
DNA forming a loose complex
- sigma factor binds to a two specific
sequences upstream of start codon
-DNA is unwound, allowing for the formation of an “open complex” -> transcription starts -> sigma factor released.
Gene expression of Bacteria: transcription termination
-Palindromic GC-rich region upstream of an AT-rich sequence.
-Once G-C rich region is transcribed -> hairpin structure forms -> causes RNA poly. to fall apart.
What are the two major subdivisions of T lymphocytes?
T-helper cells (CD4 +)
and T cytotoxic cells (CD8 +)
T helper cells (CD4 +):
-Help B cells make antibodies
-Activate macrophages and NK cells
-Help development of cytotoxic T cells
T cytotoxic cells (CD8 +):
-Recognise and kill infected host cells
-Similar to NK cells however are more specific.
T cell receptor structure:
-T lymphocyte receptor (TCR) similar to antibody -> has beta and alpha chain, hinge region, disulphide bonds, variable and constant regions.
What type of antigens do T cells recognise?
“cell-associated”, processed antigens, which have been broken down into smaller peptides
Which types of infection are T cells most effective with treating?
Viral, intracellular bacteria, and intracellular parasitic infections.
What proteins bring foreign proteins to the surface to form an MHC?
MHC proteins
Variation of MHC proteins:
MHC proteins express great variation -> because they’re the most polymorphic proteins in a human
MHC 1:
Found on all nucleated cells -> (not on RBC’s) -> display antigen to CD8 +ve T cells
MHC 2:
expressed by macrophages, dendritic cells, and B cells -> displays antigens to CD4 + T cells
T cytotoxic cell recognition of antigen:
Proteosome breaks down viral proteins -> peptides transported to the ER and bind to MHC1 -> transported to cell surface -> CD8 + T cells recognise peptide bound to MHC -> kill effected cell by induced apoptosis.
T Helper Cell recognition:
Macrophage/ dendritic cell/ b cell internalises and breaks down foreign material in endosomes -> peptides bind to MHC2 and transported to cell surface -> Activated T helper cell then helps B cells make antibodies, or produce cytokine that activate/regulate of leucocytes
