Bio 1 Exam 4 (2)

which of the following helps to hold the DNA strands apart while they are being replicated

single strand dna binding proteins

the function of dna polymerase 3 is to

add nucleotides to the 3' end of a growing dna strand

how does the enezyme telomerase meet the challenge of replicating the ends of linear chromosomes

it catalyzes the lengthening of telomeres

intervening sequences that are transcribed but not translated into protein are called

introns

many proteins are composed of several polypeptides each of which has its own gene

one gene polypeptide hypothesis

purpose of x rays in the experiment

to damage the dna, causing mutations

why is saying one gene one enzyme wrong

there are more polypeptide subunits per enzyme (Quaternary structure)

dogma of molecular biology

dna- dna in nucleus (transcription)
dna- rna in nucleus (mathalation)
rna- protein in cytoplasm (translation)

goes from rna to dna because its a retrovirus

how does HIV violate the dogma

(reverse transcriptase)

units of information

codon

characteristics of a codon

no spaces
three nucleotides (ex AUG)

function of codons

codes for a specific amino acid

how many codons actually specify amino acids

61/64

what do the other three do

they are stop codons
they cause termination of translation

several codons that code for a amino acid

degenerate

start and stop codons

start- AUG
stop- UAA UGA UAG

impact of genetic code being universal

genes can be transferred from one organism to another
cause- evolution

the telomerase enzyme would most accurately be described as a specialized

reverse transcriptase

transcription

takes dna template and makes rna
enzyme comes in , separates, makes rna, and falls off
very similar to leading strand replication of dna

three steps of transcription

initiation
elongation
termination

promoter

contains specific sequence at -35 and TATAAT at -10

dna polymerase

unwinds dna

initiation

enzyme rna polymerase binds to promoter
signals dna to unwind
now ready to make mrna

elongation

addition of nucleotides to the mrna strand
rna poly reads unwound dna strand and builds mrna

termination

rna poly crosses a stop sequence in the gene
mrna detaches from dna

dna dependent rna polymerase

mrna is made by a

distinctive features of eukaryotic transcription

multiple polymerases (each with own promoters)
transcripts are modified
termination is different
multple transcription factors

rna can't proofread like dna so rna polymerase makes a lot more mistakes. Why is this not a serious problem compared to lack of proofreading ability in dna poly.

mrna is made in large amounts and is not passed down to daughter cells like dna is so mistakes can be tolerated

why are modifications made to mrna

to protect it from being degraded

how is mrna modified

a 5 prime cap can be put on with a methal group and a poly a tail (nucleotides with adenine)

introns

sequences that interrupt the exons

exons

coding regions
genes that contain seqeunces thta form the coding sequence

eukaryotes

who has exons and introns

pre mrna splicing

process where introns are removed from primary transcript and exons are joined together by the spliceosome to produce mature mrna (occurs in nucleus)

exon shuffling

moves exons, duplicates exons. Takes parts to make new gene. (evolution)

in eukaryotes mrna processing involves all of what

addition of a 5 cap
addition of a poly a to the 3 end
pre mrna splicing
association with the spliceosome

eukaryotic mrna molecules are modified

in the nucleus

many of the copies of rna synthesized by the reverse transcriptase enzyme has mutations

the reverse transciptase carried by HIV is the most error prone dna synthesizing enzyme known. what effect does this commonly have

within a double stranded dna molecule adenine forms hydrogen bonds with T, and C forms hydrogen bonds with G. This arrangement...

permits complementary base pairing

what is the function of the 5 cap and the 3 poly a tail

protects mrna from degradation

in the process of transcription

rna is synthesized

codons are three base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare

codons are a nearly universal language among all organisms

which of the following would you expect of a eukaryote lacking telomerase

a reduction in chromosome length in gametes

according to the central dogma what molecule should go in the blank. dna- _____ - proteins

mrna

what does it mean when we say the genetic code is redundant

more than one codon can specify the addition of the same amino acid

a particular triplet of bases in the template strand of dna is 5 AGT 3. the corresponding codon for the mrna transcribed is

3 UCA 5

how does termination of translation take place

a stop codon is reached

what is not a component of the translation machinery

protein polymerase

what interrupts translation

antibotics

draw trna

powerpoint nov 18

parts of trna molecule

amino acid attachment site (where trna attaches to dna)
anticodon

a trna molecule must have a ______ and be _____ to be capable of translation

amino acid attached
charged

translation

assembly of a protein on the ribosomes using mrna to specify the order of amino acids

aminoacytl trna synthetases

molecule that does the translating in translation
reads the code in the mrna and trna
finds the trna with the right anticodon and the amino acid that finds that

why are some amino acids coded for by one or two codons whereas others by four or even six

the most common amino acids have the most codons

when you put the right amino acid on the trna it is now

charged

fewer different trna molecules exist than might have been expected for the complexity of its function. this is possible bc

the third position of the codon does not have to pair conventionally

the third nucleotide in the codon doesn't need to be paired exactly

wobble pairing
(pattern- the third base pair doesnt matter)

ribosomes
ribozyme

enzyme that catalyzes protein synthesis during translation
puts the amino acids together
and what kind of enzyme is it

during translation elongation the existing polypeptide chain is transferred to

the trna occupying the a site

sequence of events that correctly describes the initiation and elongation steps of translation in prokaryotic cells

small ribosomal subunit binds to mrna
initiator trna binds start codon on mrna
large ribosomal subunit binds
trna entry and peptidyl transfer reaction
translocation of ribosome and release of trna

a site
aminoacytl

binds to trna carrying next amino acid to be added

p site
peptidyl

binds to trna attached to the growing peptide chain

e site
exit

binds to trna that carried the previous amino acid added

a sequence of three rna bases can function as a

codon and anticodon

if the dna triplet code were atg cgt the trna anticodons would be

uac gca

in the process of transcription

rna is synthesized

translation directly requires

mrna
trna
rrna

there are 45 different kinds of trna available to serve as amino acid carriers but there are 64 mrna codons. why arent the trna anticodons and mrna codons equal in number

the third base pair on the trna allows some wobble, thus some trna anticodons can recognize more than one mrna codon

during elongation which site in the ribosome represents the location where a codon is being read

a site

post translational modifications of proteins may include the

addition of carbohydrates to form a glycoprotein

what is the mechanism of information transfer in eukaryotes

messenger rna is transcribed from a single gene and transfers information from the dna in the nucleus to the cytoplasm where protein synthesis takes place
mrna transfers info from dna to cytoplasm

which of the following is directly related to a single amino acid

the three base sequence of mrna

a single substitution mutation is least likely to be deleterious when the base change results in

a codon that specifies the same amino acid as the original codon

which of the following occurs in prokaryotes but not in eukaryotes

concurrent transcription and translation (happening at the same time)

changes in the nucleotide sequence of dna

mutations

substances that cause mutations or changes in genetic material

mutagens

mutation that alters a single base (1 nucleotide in a chromosomal dna molecule)

point mutation

types of point mutations

silent
missense
nonsense
frameshift

no effect of function bc they code for the same amino acid
caused by degeneracy in genetic code

silent

base substitution mutation that results in the alteration of a single amino acid

missense

base substitution in which a codon is changed into a stop codon. the protein is truncated bc of premature termination

nonsense

alter the reading frame in mrna downstream of the mutation. this causes protein to be too long or too short. caused by insertion or deletion of a nucleotide

framsehift

any mutation that affects the chromosomal structure

chromosomal mutations

loss of a portion of a chromosome

deletion

portion of chromosome is replicated
may have no effect if replicated region doesnt lie with a gene

duplication

when a segment of a chromosome is broken in 2 places, reversed and then put back
may have no affect

inversion

when one piece of a chromosome is broken off and joined to another chromosome
problems in meiosis and may change expression of genes

translocation

occur in a single body cell
only tissues derived from mutated cell are affected)

somatic mutation

occur in gametes and can be passed to offspring
every cell in organism is affected

germline mutation

least and worst mutation

silent
frameshift or nonsense (depends on where it occurs)

what genetic process does reciprocal translocation remind you of

crossing over
recombination
sex determination

example of a point mutation

sickle cell anemia

examples of mutagens

UV light
tar in tobacco
x rays
alcohol in beer

what is the relationship between mutations and evolution

variation
mutations generate variation

in humans the two nucleotide deletion causes a pre mature stop codon to be translated later on. This is an example of a

nonsense or frameshift

what type of nucleotide sequence would be present at the fusion site of the human chromosome 2

inactive telomere

what does the ahr gene do

codes for transcription factors which are activated by toxins
protects against harmful toxins

why would reduced sensitivity to these specific toxins provide an evolutionary advantage over non human primates
what type of mutation

resistant to fire
fire in cooking our food gives us calories to evolve
point mutation, substitution