Life 102- Exam 4

Kimberly Jeckel

Transcription Factors

Transcription Factors

• Caused by environmental stimuli

• proteins

• the proteins find their binding sites and initiate transcription of the gene that is needed

• Formed in the nucleus

Initiation

• First step of transcription

• occurs when enzyme RNA polymerase binds to a region of a gene called the promoter

• signals the dna to unwind so the enzymes cab read the bases in one of the DNA strands.

• Makes the enzyme ready to make a mRNA strand with complementary sequence of bases

Elongation

• Second step of transcription

• addition of nucleotides to the mRNA strand

• RNA polymerase reads the unwound DNA strand and builds the mRNA molecule with complementary base pairs

Termination

• Third/last step of transcrition

• occurs when RNA polymerase crosses a stop sequence in the gene

• mRNA strand is complete and detaches from DNA.

Prokaryotic Transcription

• multiple genes transcribed as ONE TRANSCRIPT

• no nucleus: transcription and translation occur simultaneously in the cytoplasm

• RNA poly binds directly to promoter

• Transcription makes mRNA(not processed)

• no introns

Eukaryotic transcription

• Carried out in the nucleus of the cell with the three sequential stages of transcription

• Transcription in nucleus-translation in cytoplasm

• DNA in nucleus, RNA travels in/out

• Transcription makes pre m-RNA —→ mRNA processing(introns removed, cap and tail added) ——> final mRNA

• Exons and introns

Point Mutation

• Change in a single nucleotide in DNA

• Usually less serious than a chromosomal alteration

• ex. changes codon UUU to UCU

Frameshift Mutation

• occurs after an addition or deletion of one or more bases to a gene

• disrupts the reading frame and will result in a completely different translation

Lac operon

• Inducible

• When a sugar is present the repressor is released so that transcription of genes involved in digestion of lactose can occur

• the presence the substrate removes the repressor and induces transcription

TRP Operon

• repressible

• the presence of the substrate (tryptophan) casues the repressor to stay bound to the DNA to repress transcription

DNA Methylation

• blocks transcription factors

• Genes ‘turn off’; nearly permanent

• caused by the attachment of methyl groups to cytosine

Dolly Method: Reprogramming

• reversal of a differentiated cell type to a undifferentiated state

• then redifferentiation into the cell type of choice in vitro

promotor

• Part of the operon

• binding site on the DNA where the RNA polymerase attaches

Basal Factors

• with RNA polymerase they bind to promoter and TATAA box

• transcription factor

Activators

• proteins that recognize specific short DNA sequences inducing the efficiency of the promotors

• transcription factor

Co-activators

• proteins required for a more efficient transcription

• dont bind to DNA

• transcription factor

totipotent

• capable of giving rise to any cell type including placental cells

• only embryonic cells within the first couple divisions after fertilization have this type of cell potency

pluripotent

• Blastocyst stage

• can give rise to all of the cell types that make up the body

mulitpotent

• adult

• capable of giving rise to all cell types of a particular tissue or organ

Stem Cells

• can replicate themselves and create new cell types

• used by scientists to leanr more about human biology and the development of therapeutics

• can show information on how diseases arise and suggest new strategies for therapy

SCNT

• somatic cell (body cel) nuclear transfer

• DNA from one cell put into egg cell w/out nucleus

• activated to grow

Telomerase

• restores telomere length

• telomeres are the ends of DNA and they become shorter every time the cell divides

Apoptosis

• type of cell death

• programmed death

• death cycle is programmed by the cell itself

Necrosis

• type of cell death

• caused by external factors such as trauma or toxins

• not programmed

Translation

• Occurs in the cytoplasm

• process by which the sequence of nucleotides in a mRNA molecule directs the incorporation of amino acids into a protein

• tRNA is able to bring amino acids to the ribosome for translation

• Has an initiation stage(binding the ribosome to the mRNA) a elongation stage(extending the polypeptide chain) and a termination stage(occurs once a stop codon is reached and the ribosome and polypeptide dissociate with the aid of release factors)

DNA base pairing

DNA: 5’ ATCG 3’

DNA: 3’ TAGC 5’

mRNA: 5’ AUGC 3’

operons

• a cluster of functionally related genes that are controlled by a shared operator

Gene regulation

• process used to control the timing, location, and amount in which genes are expressed

• Most commonly occurs during transcription when the information in a genes DNA is passed to mRNA and controls whether RNA is created or not

Operator

• Part of the operon

• binding site on the DNA where the repressor attaches

Repressor

• part of the operon

• a protein that binds to the DNA to decrease transcription

Genes

• part of the operon

• code for related enzymes in a pathway

Pre-RNA

mRNA still needs to be processed before exiting the nucleus

splices mRNA

introns(sequences not needed for protein synthesis) are spliced out of mRNA

Mature mRNA

• introns are cut out, only exons left in

• the 5’ CAp and polyA tail added (stability, movement to cytoplasm, binding to ribosome)

Codons

• 3 nucleotides (mRNA)

• Specific codons signal the start and the end of translation

• each codon can only code one amino acid

Anticodon

• 3 nucleotides complementary to mRNA

• anticodon on tRNA complementary to codon on mRNA each tRNA carries one amino acid

Template Strand

• serves as a template for transcriptio

Coding Strand

• the strand of DNA that is transcribed into RNA during gene expression

• contains thymine instead of the uracil in the RNA transcript

Mutation

• an agent of change in evolution

• changes DNA and the only mutations that matter to evolution are the ones that can be passed down to offspring

Gene Flow

• Agent of change in evolution

• movement of individuals and or genetic material from one population to another

Non-Random Mating

• Agent of change in evolution

• if individuals nonrandomly mate with other individuals in the population choices can drive evolution in a population

  • influences alleles

Genetic Drift

• Agent of change in evolution

• in each generation some individulas may leave behind a few more decendants than other individuals

  • changes allele frequency

Bottleneck effect

• happens when a random catastrophe like an earthquake kills off most of the population

• reduces genetic diversity in a population

Founder effect

• when a small group of individuals separate from a larger group and express genes that were rare in the original population

• rare genes start to become common in the next generations

• reduces genetic diversity in a population

Darwins theory of Evolution

• adaptive traits inherited (genetic)

• Evolution occurs gradually

• Occurs due to natural selection

Lamarck theory of evolution

• Acquired traits inherited ( traits you acquire during your life time can be passed down)

Natural selection

• Mechanism for evolution

• individuals that are better adapted to their environment are more likely to produce offspring

Stabilizing Selection

• Selects against traits at the two extremes and selects for traits in the middle

• type of natural selection

Directional Selection

• type of natural selection

• occurs when there is selection for traits at one extreme and not the other

Disruptive selection

• Type of natural selection

• occurs when traits at both extremes are selected for and traits in the middle are selected against

Divergent Evolution

• common ancestor

• changes in the environment cause them to adapt so they may look/act differently but they are still related

• homologous structures

convergent evolution

• No common ancestor

• organism have similar features and may act the same but are not related

• analogous structures

Evidence for evolution

1. Fossils

2. Embryology

3. Comparative anatomy

Homologous structures

• Anatomically similar but different functions

• ex. Whale flipper and bat wing

Analogous structures

• Similar function but different structure

• Ex. Insect wing, and bird wing

Hardy Weinberg equilibrium

• Situation in which a population will not see changes in allele frequencies overtime (not evolving)

• Purpose: to provide a baseline against which to measure change

• Requires:

  • Random Mating

  • No natural selection

  • no gene flow

  • no net mutation

  • very large population size

Species

• Group of organism that share genetic heritage, are able to interbreed, and to create offspring that are also fertile

Pre Zygotic Barrier

• pre mating isolating mechanism(species only mate with own kind):

  • the sperm and egg are incompatible

  • Active at different seasons

  • Individuals only mate in their preferred habitat

  • prefer members of their own species

Post Zygotic Barrier

• Post Mating isolating mechanisms:

  • Egg is fertilized but the zygote doesnt develop

  • Resulting adult is sterile

  • hybrid embryo forms but of reduced viability