Molecular Genetics Pt. 1

Everything but Biotech

DNA replication

semi-conservative - DNA unzips, one strand from parent goes into one daughter cell, other strand goes into other daughter cell

experiment by Messelson and Stahl

helicase + others

enzyme that unzips the DNA

topoisomerase: makes knicks in the backbone to relieve tension

SSBs: hold the DNA apart so that nitrogenous bases don’t make hydrogen bonds again

produces replication fork

primers

specific areas along DNA strands are primer sites where primers bind and start replication

DNA polymerase III goes from 5’-3’ (leading strand) but can only add nucleotides to the 3’ end

RNA primers will start the synthesis of new providing starting point for DNA polymerase III

lagging strand

3’-5’ direction

has discontinued pieces called Okazaki fragments that are later linked together by DNA ligase

DNA polymerase removes RNA primers and fills in gaps with DNA

proof-reading enzymes

estimated 1 out of 10,000 basepairs has mismatch during first run-through

after, mismatch is 1 out of every billion nucleotides

mismatch repair: polymerase removes incorrect nucleotide and adds proper one

excision repair: section is cut out and gap is filled by DNA

telomers

specialized structures composed of short repeated sequences of DNA made from telomerase

protect chromosome ends from deterioration or fusion with neighboring chromosomes

transcription

DNA being transcribed into an intermediary - mRNA

occurs in nucleus

initiation, elongation, termination

Initiation

RNA polymerase attaches to promoter region of DNA (TATA box)

transcription factors bind to promoter to help RNA polymerase initiate transcription

some act as enhancers, others as repressors

Elongation

RNA polymerase adds appropriate RNA nucleotide to 3’ end of growing strand

Termination

region where polymerase should stop so mRNA is release and set free

prokaryotic DNA replication

once mRNA produced by transcription, translation already occurs - polyribosomes

modifications to mRNA

5’ end has methyl cap to protect mRNA, 3’ end has poly-A tail to ease movement from nucleus to cytoplasm

introns: noncoding regions are removed by the splicosome

exons: coding regions glued back together by splicosome

genetic code

conversion of nucleotides to amino acids through codons (pairs of three nucleotides)

64 different combinations of codons

start codon: AUG (met)

stop codons: UGA, UAG, UAA

tRNA

carry amino acids to ribosomes

each ahs anticodon to complement on the mRNA

enzyme aminoacyl tRNA synthase attaches the amino acid to tRNA

wobble

uracil in third position of anticodon can pair with A or G

This allows for variability in codon-anticodon pairing, making the genetic code more flexible

ribosome

large subunit containing A and P site

P site: holds the tRNA carrying the growing polypeptide chain

A site: tRNA holding next amino acid

peptide bonds formed between amino acids into polypeptide chain

translocation

A site becomes P site because of how ribosome is moving

termination

no anti-codon for termination signal codon, ribosome simply stops translocating

operator

short sequence near the promoter that assists in transcription by interacting with regulatory proteins

operon

promoter/operator pair that services multiple genes

ex: lac-operon

repressor

prevents RNA polymerase from binding to active site

enhancer

DNA region known as “regulator” located thousands of bases away from promoter, influences transcription by interacting with specific transcription factors

inducer

molecule that binds to and inactivates repressor

mechanisms for control of gene expression in eukaryotes

• initiation of transcription

• RNA splicing

• passage through nuclear membrane

• protein synthesis

• RNA interference

• protein degradation

turned on vs. turned off

on: methylation of DNA

off: acetylation of DNA

induction

influence of one group of cells on the development of another through physical contact or cell signaling

cytoplasmic distribution

asymmetry contributes to cell differentiation and function since different areas have different amounts of cytoplasm

homeotic genes

regulatory genes that determine how segments of an organism will develop

mutations

heritable change in genes of an organism

point mutations: alter a single base (ex sickle cell)

frameshift: deletion or addition of DNA nucleotides that is not in pairs of 3

missense: substitution of wrong nucleotides, will cause addition of amino acids to chain

nonsense: substitution that creates a premature stop codon

thymine dimers: two adjacent thymine bases bonded together, often caused by UV radiation

chromosomal mutations

change structure of chromosomes

deletion: loss of segment

duplication: duplicated segment

inverted: segment is reversed in orientation

reciprocal translocation: one part of chromosome is broken and becomes part of another chromosome

virus

parasitic infectious agent that requires a host

classification based on genetic material, capsid, presence of viral envelope (produced in ER), and host range

all have genome (DNA/RNA) and protein coat (capsid)

retrovirus

RNA virus carrying reverse transcriptase

will reverse transcribe info from RNA to DNA mRNA from this process will rise to retrovirus offspring, leaving cell in lytic pathway

ex: HIV

lytic and lysogenic pathway

lytic: cell produces viral offspring, released from cell, killing host

lysogenic: virus dormant and incorporates its DNA into cell’s DNA as a provirus - quietly reproduced

viroids and prions

viroids: small plant viruses

prions: incorrectly folded form of a brain cell protein, converts normal host proteins to misshapen ones

transformation

uptake of foreign DNA from surrounding environment

proteins on surface of cells that snag pieces of DNA from around the cell that are from closelt related species

heat-killed S virulent strain mixed with non-virulent live R strain would make R strain virulent

transduction

phage: virus that transmits bacterial DNA

transduction: movement of genes from one cell to another by phages

generalized and specialized

generalized transduction

a process where a bacteriophage can transfer any bacterial gene from one bacterium to another, leading to genetic variation.

specialized transduction

a process where a bacteriophage transfers specific bacterial genes from one bacterium to another, resulting in the incorporation of those genes into the new host's genome.

conjugation

the process by which one bacterium transfers genetic material to another through direct contact, often via a sex pilus.