Molecular Genetics

anti parallel

run in opposite directions

origin of replication

specific sequence on a DNA molecule where replication begins

replication bubble

open region of DNA where replication occurs when helicase enzymes separate two parental strands at ORI

replication fork

ends of Replication Bubble

helicase

enzyme that breaks hydrogen bonds and unzips molecules

single-stranded binding proteins

bind to unpaired DNA strands to keep them from re-pairing

topoisomerases

break bonds ahead of replication fork to relieve strain and prevent supercoiling as DNA unzips

RNA primers

provides a 3’-OH group that allows for DNA polymerase to begin DNA replication

RNA primase

RNA polymerase that synthesizes short RNA primers on single-stranded DNA

DNA polymerase III

attaches at primer and moves along DNA from 3’ towards the 5’ end. reads existing DNA single strand and pairs up free complementary nucleotides with them

leading strand

built continuously following helicase away from origin of replication and toward the fork

lagging strand

built in Okazaki fragments in the opposite direction as the fork keeps moving

DNA polymerase I

removes RNA primers and replaces them with DNA nucleotides

DNA ligase

“glue” that joins sugar-phosphate backbones of Okazaki fragments into continuous DNA strand

mismatch repair

enzymes remove and replace incorrectly paired nucleotides resulting from replication errors

nucleotide excision repair

damaged DNA segment cut out (excised) by a nuclease and gap filled with nucleotides using undamaged (complementary) strand as template

telomeres

repeating code at ends of strand that shorten after replication

telomerase

can extend telomeres

genetic engineering

Insert new gene into organism’s gene

Polymerase Chain Reaction

amplify DNA

Gel Electrophoresis

Use restriction enzymes to cut DNA → separate by size to compare

CRISPR

Can introduce a segment from a functional gene, which will be used as a template by repair enzymes to edit defective gene so it’s corrected

mRNA

• “messenger”

• copy of DNA for a gene that goes to a ribosome

tRNA

• “transfer”

• bring amino acids to ribosome

• complementary to codon (mRNA)

rRNA

• “ribosomal”

• makes up part of the ribosome

transcription

read DNA sequence of a gene on template strand using RNA polymerase and make RNA transcript

promoter

specific DNA sequence where RNA Polymerase attaches and initiates transcription

transcription factors

in eukaryotes, a collection of proteins mediate the binding of RNA polymerase and the initiation of transcription

introns

• noncoding DNA

• “interrupt” code

exons

• coding DNA

• “expressed”

• “exit the nucleus”

5’ cap

• facilitate export of mature mRNA from nucleus

• help ribosomes attach to 5’ end

3’ Poly-A Tail

protect mRNA from degradation by hydrolytic enzymes

alternative splicing

splice different combinations of exons to create different shaped proteins (ex. antibodies)

translation

read mRNA code using ribosomes to produce polypeptides

wobble

mutation where 3rd base of codon can change and may not affect amino acid

post-translational modifications

after translation, polypeptide may be modified in many ways before it becomes a final protein

• enzymes may remove one or more amino acids from leading end of polypeptide chain

• enzymes may cleave polypeptide chain into 2 or more piecces

• may join up with other polypeptides (quaternary structure)

• may get sugars phosphate groups

point mutations

changes in DNA

silent

new codon is swapped out for a different one

missense

changes the amino acid. may or may not affect protein (depends on R group properties)

nonsense

changes a codon in the middle to a STOP codon

frameshift

addition or deletion/removal of 1+ nucleotides

operons

a group of genes in a region of a prokaryotic chromosome that can be controlled in a unified manner

operator

on/off switch where repressor protein binds to prevent transcription

strucutral genes

sequences that actually code for proteins (usually enzymes)

regulatory gene

(located anywhere on a chromosome) codes for repressor protein, which controls gene expression

inducible operon

normally off, but can be turned on when needed

lac operon

bacteria’s ability to break down lactose in glucose-deprived environment

repressible operon

normally on, but can be turned off when not needed

trp operon

bacteria make tryptophan from precursor molecule when nutrient medium lacks this amino acid

epigenetics

inheritance of traits transmitted by mechanisms not directly involving nucleotide sequence of a genome

histone acetylation

+ acetyl groups to histones → DNA unwind/loosen → turns genes on

DNA methylation

+ methyl groups to DNA → DNA wind tighter → turns genes off (long-term inactivation)

microRNA and Small Interfering RNAs

small RNA molecules that regulate gene expression by degrading mRNA or blocking translation