Bio exam 3

constituitive proteins

always active (require most amount of energy)

proteins made in inactive state

can be activated in presence of an enzyme

translational control (prokaryotic)

some genes are transcribed and not translated

transcriptional control (prokaryotic)

some genes are never transcribed (least energy required)

negative control

regulatory protein is a repressor

positive control

regulatory protein is an activator

inducible operon

normally off, must be turned on (catabolic)

repressible

normally on, must be turned on (anabolic)

catabolic

breakdown

anabolic

synthesis

repressor

binds to operator to stop transcription

inducer

binds to repressor to change its shape so it can no longer bind with operator (inducible)

corepressor

activates repressor so it can bind to operator and stop transcription (repressible)

activator (prokaryotic)

binds to activator binding site to cause transcription

substrate

binds to activator to activate it and cause transcription (inducible)

product

binds to activator to change it’s shape so it can no longer bind to activator binding site (repressible)

lac operon

negative control, inducible

• repressor: lac repressor

• inducer: alolactose

trp operon

negative control, repressible

• repressor: trp repressor

• corepressor: tryptophan

Catabolite activator protein (CAP)

binding upstream of promoter results in stronger binding of RNA polymerase to DNA template and maximum transcription

cyclic AMP activates CAP protein

low glucose —> more cyclic AMP —> more activated CAP —> maximum transcription

transcriptional regulation (eukaryotic)

determines when genes are transcribed (chromatin, DNA)

post-transcriptional regulation

determines types and availability of mRNAs to ribosome (pre-mRNA, mature mRNA)

translational regulation

determines rate at which proteins are made (initiation of protein synthesis)

post-translational regulation

determines availability of finished proteins (new polypeptide chains, finished proteins, protein breakdown)

histone acetyltransferase

acetylation by HA breaks interaction between DNA and histone tails

histone deacetylase

deacetylation by HD causes acetyl groups detach so tails bind to DNA

regulation by activators

• enhancer contains enhancer regulatory sequences

• activators bind to enhancer regulatory sequences

• coactivators bind to activators at enhancer and to proteins at proximal region creating a loop which leads to maximum transcription

steroid hormone regulation of gene expression

1. steroid hormone binds to previously inactive steroid hormone receptor, activating it

2. complex moves into nucleus

3. complex attaches to steroid hormone response element, causing maximum transcription with no regulation

microRNAs/RNA interference

1. microRNAs form hairpin loops

2. loop is transported out of nucleus into cytoplasm

3. dicer protein removes end of loop (lariat) leaving dicer + dsRNA

4. protein complex attaches

5. protein complex degrades one strand of dsRNA creating the miRNA induced silencing complex

6. miRISC binds with mRNA that has complimentary sequences (imperfect pairing)

7. mRNA cannot be translated because RNA is unstable

• mRNA bound with miRISC preserves it for longer

short interfering RNAs

• viral origin

1. microRNAs form hairpin loops

2. loop is transported out of nucleus into cytoplasm

3. dicer protein removes end of loop (lariat) leaving dicer + dsRNA

4. protein complex attaches

5. protein complex degrades one strand of dsRNA creating the miRNA induced silencing complex

6. binding with miRISC results in perfect pairing and mRNA is destroyed

transcription specificity in eukaryotes

• activators are unique to genes, so presence of specific activators and enhancers determine which genes are transcibed

  • expression of activators is in some response to external stimuli

activators (eukaryotes)

• position RNApol

• release RNApol from promoter

• accelerate binding and assembly of general transcription factors

• activating coactivators

repressors (eukaryotes)

• mask activation site

• interfere with general transcription factors

• remodel chromatin

particulate theory of inheritance

Mendel - characteristics are passed on to offspring in discrete hereditary factors (genes)

principle of segregation

Mendel - two alleles of a gene segregate from each other during gamete formation

reciprocal cross

reversing sex of parents for a given trait to test if it is sex-linked

test cross

crossing individual with unknown phenotype and individual with known phenotype (often recessive)

selfing

crossing between 2 individuals from same generation

backcross

crossing one offspring with parent

incomplete dominance

heterozygous individuals have intermediate phenotype, related to gene expression

codominance

both alleles are expressed in heterozygous individuals

multiple alleles

gene has more than 2 alleles that exist in the population

epistasis

effect of one gene masks expression of another gene

• recessive: 2 recessive alleles mask expression of second gene

• dominant: one dominant allele masks expression of second gene

polygenic inheritance

a trait is controlled by multiple genes

pleiotrophy

one gene having multiple cascading effects

Thomas Hunt Morgan

established autosomal linkage and sex linkage

recombination frequency

(total # recombinants/total offspring) x 100 = rf

deletion

segment lost from a chromosome

duplication

segment is broken from one chromosome and inserted into its homolog, adding to the ones already there

translocation

segment is attached to a different, nonhomologous chromosome

inversion

segment reattaches to same chromosome, but in reversed orientation - order of genes is reverses

Implications of Hardy Weinberg law

1. Reproduction alone does not change allele frequencies

2. Allele frequencies can be used to determine genotypic frequencies only if population is in HW equilibrium

3. A single generation of random mating produces equilibrium genotypic frequencies

4. If a population is not in HW equilibrium, one of the assumptions has been violated.

Conditions necessary for HW to be in effect

1. no mutation

2. no migration

3. large population

4. all organisms are equally fit

5. random mating

Measures of population variation

1. variance in allele frequency

2. observed heterozygosity

Forces of microevolution

1. mutation

2. gene flow

3. genetic drift

4. natural selection

5. nonrandom mating

Mutations

increases variability

Gene flow

movement of genes into and out of a population

• migration increases variation within new population and decreases variation within original population

• homogenizes gene pool between populations

genetic drift

fluctuations in frequency of alleles in a population

small populations are more prone to drastic changes in gene pool than large populations

genetic bottleneck and founder effect

genetic bottleneck

large gene pool in original population, but gene pool in surviving population is more restricted

founder effect

small number of individuals migrate out of a population to start a new population

nonrandom mating

selecting mate with particular phenotype and underlying genotype

inbreeding

inbreeding

genetically related individuals mate with each other

increases frequency of homozygous phenotypes and decreases frequency of heterozygotes, so recessive phenotypes are often expressed

morphological species concept

individuals of a species share measurable physical traits that distinguish them from individuals of other species

pros: applies for sexual and asexual species, applies for fossils

cons: members of same species can look very different, convergent evolution

biological species concept

reproductive isolation: organisms are separate species if they’re unable to reproduce viable offspring

pros: very applicable to real world situations

cons: hybrids

phylogenetic species concept

cluster of populations that emerges from same small branch (evolutionary relationships)

pros: applicable to all organisms

cons: over classification

ecological species concept

based on where and how organisms live

pros: works for all types of organisms

cons: unclear definitions of ecological niches, convergent evolution

subspecies

members or a species exhibit dramatic, easily recognized phenotypic variation

ring species

plant and animal species with ring shaped geographical distribution surrounding uninhabitable terrain

clinal variation

species distributed over a large, environmental diverse area may exhibit a pattern of smooth variation in traits along a geographical gradient

allopatric speciation

physical splitting of a population

adaptive radiation

rapid speciation from a single ancestor

secondary contact

3 options:

• species remain separate and distinct

• hybrid zones

• interbreeding merging back into single species

sympatric speciation

reproductive isolation evolves between distinct subgroups that arise within one population

autopolyploidy

• single species

• through error in meiosis, doubling of chromosomes produces diploid gametes, and fertilization of one diploid gamete by another produces a tetraploid zygote

• tetraploids are reproductively isolated from diploid population

allopolploidy

2 closely related species hybridize and form polyploid offspring, hybrid offspring are sterile if chromosomes of the two parent species do not pair properly during meiosis

prezygotic isolation

operates before production of fertilized egg, preventing egg and sperm from coming together

ecological isolation

living in different habitats in same region

temporal isolation

reproduction takes place at different times of year, so change of exchanging genes is very low

behavioral isolation

signals of one species are not recognized by another

mechanical isolation

differences in structure of reproductive organs or other body parts physically prevent mating

gametic isolation

species have nonmatching receptors on gametes

postzygotic isolating mechanisms

operates after zygote formation, reducing fitness of hybrids

hybrid inviability

offspring don’t survive

hybrid sterility

offspring are viable but sterile

hybrid breakdown

offpsring have reduced survival and reproduction