Biology DAT Ch. 6-10 Flashcards
Nucleosomes
are complexes of DNA wrapped around histone proteins.
Each nucleosome has
9 histones total. The central core contains 2 of each histone H2A, H2B, H3 and H4. On the outside, a single histone H1 holds the DNA in place.
Chromatin
refers to the overall packaging of DNA and histones.
Two types of chromatin
Euchromatin and heterochromatin
Euchromatin
nucleosomes are “loosely packed”, so DNA is readily accessible for transcription.
Heterochromatin
nucleosomes are “tightly packed”, so DNA is mostly inactive.
Histones
are positively charged while DNA is negatively charged, allowing proper binding.
Deacetylation
of histones increases positive charges, tightening DNA histone attractions and decreasing transcription.
Methylation
of histones adds methyl groups, either increasing or decreasing transcription.
Origin of replication
replication is required to initiate DNA replication, where the DNA strands first separate. Organisms w circular DNA (bacteria) have a single origin of replication while organisms with linear DNA such (humans) have multiple origins of replication.
Semiconservative replication
where each new double helix produced by replication has one “new” strand and one “old” strand.
DNA
DNA is antiparallel, the 5’ end (terminal phosphate group) of one strand is always next to the 3’ end (terminal hydroxyl group) of the other strand and vice versa.
Initiation replication
creating origins of replication at
A-T rich segments of DNA because they only have 2 Hydrogen bonds.
Elongation
producing new DNA strands using different types of enzymes.
Elongation enzymes
helicase, single-stranded binding proteins, topoisomerase, DNA polymerase, primase, sliding clamp proteins, RNA primers, DNA ligase
Helicase
unzips DNA by breaking hydrogen bonds between strands, creating the replication fork
Single-stranded binding proteins
bind to uncoiled DNA strands, preventing reattachment.
Topoisomerase
nicks the DNA double helix ahead of helicase to relieve built-up tension.
DNA polymerase
adds free nucleoside triphosphates to 3’ ends.
Primase
places RNA primers at the origin of replication to create 3’ ends for nucleotide addition.
Sliding clamp proteins
hold DNA polymerase onto the template strand.
Leading strand
is produced continuously because it has a 3’ end that
faces the replication fork.
Lagging strand
is produced discontinuously because its 3’ end is facing
away from the replication fork. Thus, RNA primers are needed to produce Okazaki fragments.
Okazaki fragments
short DNA fragments
DNA ligase
glues separated fragments of DNA together.
Termination
replication fork cannot continue, ending DNA replication.
Telemores
are noncoding, repeated nucleotide sequences at the ends of linear chromosomes.
Telomerase
is an enzyme that extends telomeres to prevent DNA loss, prevents critical information from being lost.
Genes
are instructions within DNA that code for proteins. Must first be transcribed into RNA before being translated into proteins.
messenger RNA
DNA undergoes transcription to produce single-stranded messenger RNA (mRNA).
Transcription
initiation (promoter sequence attracts RNA polymerase to trasncribe the gene), elongation, termination (signals RNA polymerase to stop transcribing)
Transcription bubble
forms during elongation and RNA polymerase travels in the 3’–>5’ direction on the template strand, it extends RNA in the 5’–>3’ direction
Prokaryotes: Before transcription occurs, a sigma factor combines with…
prokaryotic core RNA polymerase to form RNA polymerase holoenzyme, giving it the ability to target specific DNA promoter regions.
Prokaryotes: Operon
is a group of genes that is controlled by one promoter, functioning as a single unit.
Prokaryotes: Operator region
is present near the operon’s promoter and binds activator/repressor proteins to regulate the promoter.
Prokaryotes: lac operon
is an inducible operon (must be
induced to become active). LacZ, lacY, and lacA are the 3 genes contained within the lac
operon that encode proteins required for lactose metabolism. The lac operon will only be induced when glucose is not available as an energy source, so lactose must be used.
Prokaryotes: lac repressor protein
is the first way that the lac operon is controlled. This protein is encoded by an entirely separate gene called lacI, which is constitutively expressed (always on). Thus, the lac repressor protein is always bound to the operator, blocking transcription.
Prokaryotes: Constitutively expressed
always on
Prokaryotes: Lactose is present
it is converted to allolactose.