My Exam #3 - Bio 133 - PSU

Transcription

DNA to mRNA

Where is mRNA transcribed?

Nucleus

Transcription factors

proteins that bind to the promoter region of DNA to initiate transcription (RNA polymerase binds to make mRNA)

What initiates transcription?

transcription factors

Transcription steps

1. initiation: Binding of transcription factors and RNA

   polymerase to promoter

2. Elongation: RNA polymerase adds nucleotides in 5’ → 3’

   direction

3. Termination: terminator sequence is reached

mRNA

copy of gene - goes to ribosome

RNA processing

• happens before leaving the nucleus

• Add 5’ cap and 3’ poly-A tail

• remove introns and join exons

exons

are expressed

introns

discarded

RNA structure

• single stranded

• ribose = sugar

• U instead of T

Translation

mRNA to polypeptide

Where does translation take place?

at ribosomes

Translation steps

1. Initiation: mRNA, small ribosomal unit, and tRNA come together

2. Elongation: large subunit attaches, tRNA molecules bring AA to ribosome, AA is attached

3. Termination: stop codon reached

tRNA

anticodon complementary to codon on mRNA; carries amino acids to ribosomes

GENETIC CODE TRAITS: redundant

multiple codons (UCA, UCC, UCU) can code for the same amino acid (Ser)

GENETIC CODE TRAITS: unambiguous

each codon specifies only one amino acid (ACU codes ONLY for Thr)

GENETIC CODE TRAITS: universal

all codons specify the same amino acid in all organisms (genetic code is the same for cats and humans)

epigenetics

control of gene expression; “above the gene”

epigenetic changes

• do not change DNA sequences

• do change chemical groups associated with DNA

• can be passed to new generation

True or false: Epigenetics changes the DNA sequence

False

True or false: You can inherit epigenetic patterns

true

global chain switching

subunits of hemoglobin differ in embryo, fetus, and adult

embryo hemoglobin

epsilon and zeta (embryo, epsilon; ze pregnant lady)

fetus hemoglobin

gamma and alpha (noelle is just a baby [gamma phi] and she’s the alpha)

adult hemoglobin

alpha and beta (me and mom are adults, I am alpha and she”s beta)

Why do we globin switch?

to meet changing oxygen needs; fetal blood has a higher affinity for oxygen, allowing the fetus to extract oxygen from maternal blood

histones

proteins around which DNA entwines; expose DNA to allow transcription

chromatin remodeling

acetyl groups turn on transcription (athletes turn me on)

methyl groups turn off transcription (men turn me off)

alternative splicing

exons shuffled into unique arrangements to produce different proteins

protein modifications

different chemical groups (sugars and lipids) added to base protein

protein splicing

a single protein is cut in two

metacentric chromosome

centromere is in MIDDLE of chromosome

sub-metacentric chromosome

centromere is off of middle by a liitle

acrocentric chromosome

centromere is at top of chromosome (leaves acorn looking arms)

point mutation

change in a single DNA base

silent mutation

no effect on phenotype

missense mutation

replaces one amino acid with another

nonsense mutation

changes a codon for amino acid into a stop codon - resulting protein is too short (no = stop)

deletions and insertions

removal or addition of several DNA bases

frameshift mutation

adding or removing bases throws off reading frame of protein synthesis machinery (literally shifts the frame of protein)

conditional mutation

a mutation that affects the phenotype only under certain conditions (ex. G6PD, triggered by fava beans, sulfa drugs, or infections)

Why are mutations harmful?

Protein is changed, leading to disease

Mice epigenetics example

All mammals have a gene called agouti. When a mouse's agouti gene is completely unmethylated, its coat is yellow and it is obese and prone diabetes and cancer. When the agouti gene is methylated (as it is in normal mice), the coat color is brown and the mouse has a low disease risk. Fat yellow mice and skinny brown mice are genetically identical. The fat yellow mice are different because they have an epigenetic "mutation."

When researchers fed pregnant yellow mice a methyl-rich diet, most of her pups were brown and stayed healthy for life. These results show that the environment in the womb influences adult health. In other words, our health is not only determined by what we eat, but also what our parents ate.

allelic disorders

different disease phenotypes caused by mutations in same gene; result from mutations in different parts of the gene (ex. sickle cell, beta thalassemia)

sickle cell and beta thalassemia

are both due to mutations in the beta-globin gene (hemoglobin is a protein comprised of 2 alpha-globin and 2 beta-globin chains). Allelic disorders result from mutations in different parts of the same gene.

beneficial mutations

mutations that benefit the organism; lead to new versions of proteins that help organisms adapt to changes in their environment; essential for evolution to occur

spontaneous mutations

generated spontaneously (random mistake in DNA replication)

induced mutations

chemicals or radiation

DNA proofreading

DNA polymerase reads the newly added base, ensuring that it is complementary to the corresponding base in the template strand before adding the next one

mismatch repair

proofreading enzymes remove mismatched bases

excision repair

enzymes cut out segments of DNA with mistake

chromosome abberations

large scale changes that have effects on health

cytogenetics

matching of phenotype to detectable chromosomal abnormalities

karyotype

images of metaphase chromosomes organized according to size

At what stage do we view chromosomes

metaphase when chromosomes are condensed

tests during pregnancy: amniocentesis

removal of fetal cells at 14-16 weeks; causes miscarriage in 1/1600 cases

tests during pregnancy: chorionic villus sampling

removal of fetal cells from chorionic villi at 10-12 weeks; greater risk of miscarriage

polyploidy

extra sets of chromosomes

aneuploidy

one missing chromosome or one extra chromosome

trisomy

an extra chromosome (ex. trisomy 21=down syndrome, trisomy 18=edward syndrome)

monosomy

a missing chromosome

turner syndrome

XO females (missing another X), delays sexual development

klinefelter syndrome

XXY males; delays sexual development, causes long limbs

XXY

causes tallness and acne, falsely linked to violent behavior

uniparental disomy

inheriting both copies of a chromosome from one parent (rare); arises from 2 nondisjunction events or a trisomy with subsequent chromosome loss

population

individuals of same species in same area

gene pool

all the alleles in a population

evolution

change in genetic structure of a population

nonrandom mating

mating is not random (ex. arranged marriage)

migration

gene flow between two previously isolated populations

genetic drift

changes in allele frequencies due to chance (in small populations)

mutations

create new alleles, most have harmful effects

natural selection

limited resources, differential reproductive rates, those with advantageous traits survive and reproduce (this is different from artificial selections which is intentional breeding for certain traits; ex. pugs, french bulldogs)

Hardy-Weinberg principle

allele and genotype frequencies stay constant unless disturbed (population stays in equilibrium and does not evolve)

allele frequencies

p + q = 1

freq of dominant allele (A) = p

req of recessive allele (a) = q

genotype frequencies

p^2 + 2pq + q^2 = 1

freq of homozygous dominant (AA) = p^2

freq of heterozygote (Aa) = 2pq

req of homozygous recessive (aa) = q^2