Chapter 5b - The Central Dogma Revisited Flashcards
DNA -> mRNA
transcription
where does mRNA leave through
nuclear pores
mRNA -> protein
translation
used to synthesize proteins
ribosome
model of DNA replication in humans
semiconservative
direction of synthesis during DNA replication
5’ to 3’ direction
needed for initiation
primer
- enzymes and proteins needed in DNA replication
- large protein complex that carries out DNA replication, starting at the replication origin
replisome
allows each strand of DNA to serve as a template for a new strand
base pairing
- in DNA, adenine (A) forms a base pair with thymine (T) using two hydrogen bonds, and guanine (G) forms a base pair with cytosine (C) using three hydrogen bonds
- in RNA, thymine is replaced by uracil (U)
Watson–Crick base pairing
- labeled “parent” nucleotides in DNA strands with heavy nitrogen = 15N
- label new nucleotides with lighter isotope = 14N
Meselson & Stahl
Models of DNA replication
- conservative
- semiconservative
- dispersive
parental double helix remains intact and all new copy is made
conservative
two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand
semiconservative
each strand of both daughter molecules contains a mixture of old and newly synthesized parts
dispersive
how are base pairs bonded
hydrogen bonding
the initiating point that generates a replication bubble
origin of replication
unwound and open region of DNA where DNA replication occurs
replication bubble
region where a cell’s DNA double helix has been unwound and separated to create an area where DNA polymerases and the other enzymes involved can use each strand as a template to synthesize a new double helix
replication fork
formed at all potential origins of replication through the action of the origin recognition complex (ORC), Cdc6, Cdt1, and the Mcm2-7 complex
pre-replicative complex (pre-RC)
powers nucleotide addition
pyrophosphate hydrolysis
bond between two nucleotides (sugar-phosphate)
phosphodiester bond
Different DNA Polymerases
- DNA polymerase I
- DNA polymerase II
- DNA polymerase III
DNA polymerase I
- 5’-3’ polymerization
- 3’-5’ proofreading
- 5’-3’ exonuclease activity
DNA polymerase II
- DNA repair functions
- restarts replication after damaged DNA halts synthesis
DNA polymerase III
primary replication enzyme
DNA polymerase IV
- 5’-3’ polymerase activity
- DNA repair
DNA polymerase V
- 5’-3’ polymerase activity
- DNA repair
- translesion DNA synthesis
how are incorrect nucleotides removed
3’-5’ proofreading
pair of abnormally chemically bonded adjacent thymine Bases in DNA, resulting from damage by ultra-violet irradiation
thymine dimer
cuts the damaged DNA strand at two points and the damaged section is removed
nuclease
repair synthesis and fills in missing nucleotides
DNA polymerase
seals the free end of the new DNA to the old DNA, making the strand complete
DNA ligase
unwinds parental double helix at replication forks
helicase
binds to and stabilizes single-stranded DNA until it can be used as a template
single-strand binding protein
corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
topoisomerase
synthesizes a single RNA primer at the 5’ end
primase
elongates strand, adding on to the primer
DNA polymerase III
removes primer from 5’ end of strand and replaces it with DNA, adding on to the adjacent 3’ end
DNA polymerase I
joins the nicks in DNA strand
DNA ligase
both daughter strands are laid down in the ___ direction
5’ to 3’
transcribed DNA strand
template strand
untranscribed DNA strand
coding strand
untranscribed DNA strand = __ RNA
same sequence as RNA
- region containing the RNA polymerase, DNA, and the RNA product
- molecular structure formed during DNA transcription when a limited portion of the DNA double helix is unwound
- size ranges from 12 to 14 base pairs.
transcription bubble
enzyme used in making mRNA
RNA polymerase
Steps in Transcription
- Initiation
- Elongation
- Termination
RNA polymerase binds to promoter sequence on DNA
Initiation
Role of promoter
- starting point
- template strand
- direction on DNA
direction on DNA when transcribing
- always read DNA 3’-5’
- build RNA 5’-3’
Components of RNA polymerase holoenzyme
- 2 αββ’ - core enzyme
- (2 αββ’) δ - RNA polymerase holoenzyme
- these proteins bind to genes at sites known as enhancers
- help to determine which genes will be switched on, and they speed the rate of transcription
activators
site where activators bind to
enhancers
- these proteins bind to selected sets of genes at sites known as silencers
- interfere with the functioning of activators and thus slow transcription
repressors
sites where repressors bind to
silencers
these “adapter” molecules integrate signals from activators and perhaps repressors and relay the results to the basal factors
coactivators
in response to injunctions from activators, these factors position RNA polymerase at the start of the protein-coding region of a gene and send the enzyme on its way
basal factors
- define the direction of transcription and indicate which DNA strand will be transcribed;
- this strand is known as the sense strand
Promoter sequences
Promoter sequences are also known as __ __
sense strand
stop site of transcription
terminator
RNA polymerase copies DNA as it unwinds
elongation
how many base pairs are transcribed at a time
~20 base pairs
simple proofreading during elongation stage in transcription
- 1 error/10^5 bases
- make many mRNAs
- mRNA has short life
- not worth editing
direction of transcription
- “downstream”
- reads DNA 3’-5’
where does RNA polymerase stop
termination sequence
refers to two areas of a DNA strand whose base-pair sequences are inverted repeats of each other
Dyad symmetry