protein synthesis Flashcards
what did Garrod suggest genes coded for?
enzymes
according to garrod, what accounted for symptoms of inherited diseases?
if a person lacked a particular enzyme
what did Beadle and Tatum work with?
mutants of red bread mold called Neurospora
what did Beadle and Tatum discover?
wild type could grow on minimal media
however, 3 auxotrophs could not survive on minimal media because they had a mutated gene that coded for a particular enzyme in a metabolic pathway to make arginine as the final product
what are auxotroph?
mutant strains
what hypothesis came from Beadle and Tatum?
one gene, one enzyme hypothesis
what was Beadle and Tatum’s hypothesis changed to? why?
one gene, one protein
to account for the fact that not all genes code for enzymes, but all genes do code for proteins
what is the bridge between DNA and protein synthesis?
RNA
3 differences between RNA and DNA
RNA has ribose, not deoxyribose
RNA has uracil, not thymine
RNA is single stranded in protein synthesis
what does transcription involve?
using DNA as a template to build mRNA which gets modified before leaving the nucleus to a ribosome
what happens once mRNA is at the ribosome?
translation can begin
in what “language” is DNA/RNA written in?
5 nucleotides
in what “language” is protein written in?
20 amino acids
what happens in translation?
language of DNA/RNA is translated into language of protein
amino acids are linked to form protein
how much of DNA is used in the making of mRNA?
one half
nucleotide triplet
codon
what is de-coded into an amino acid?
a codon
how is genetic code universal?
its shared by everything from most bacteria to plants and animals
what does the shared language of genes show?
provides evidence of of a common ancestor of all modern organisms
since genetic code is the same in all organisms, what can we do with it?
insert human genes into bacteria and make many important proteins from medical uses like insulin (HGH- human growth hormone)
what is the enzyme responsible for pulling DNA apart and bring in RNA nucleotides?
RNA polymerase
what are the three types of RNA?
mRNA - messenger
tRNA - transfer
rRNA - ribosomal
what is each type of RNA built by?
a different RNA polymerase
what three parts is transcription split into?
initiation
elongation
termination
what does transcription begin with?
a collection of proteins called transcription factors binding to the TATA box on the DNA molecule
where and what is the TATA box?
is in the promoter region of the DNA molecule and it is where the RNA polymerase (II) will bind
in which direction does RNA polymerase move along the DNA molecule?
3 to 5 so that mRNA can grow in its 5 to 3 direction
what happens to DNA after RNA polymerase moves past a region of the DNA molecule?
it reforms back into a double helix
how many RNA polymerases are there working on a DNA molecule at a time?
several
why are there many RNA polymerases?
to increase the number of mRNA molecules being made
when does RNA polymerase continue to add RNA nucelotides?
until it transcribes a terminator - UAA/UAG/UGA
AND mRNA is cut free from the enzyme
before mRNA can leave the nucleus, what happens to it?
it gets modified/RNA processing
what does the 5’ end of mRNA get?
5’ cap made up of modified guanine and 3 phosphates
what does the 3’ end of mRNA have?
poly (A) tail made of 20-200 adenine
what is the function of adding the “cap and tail” molecules to the end of mRNA?
to protect the mRNA from getting broken down by enzymes and it helps the mRNA attach itself to a ribosome
what enzyme modifies mRNA?
spliceosome
what does spliceosome do?
RNA splicing- a cut and past job of the mRNA molecule, cutting the noncoding stretches of nucleotides
noncoding segments that do not code for amino acids
introns
coding segments
exons (expressed)
what pastes together the coding segments?
spliceosome
what is ribosome made of?
large subunit and small subunit
rRNA and proteins
when is the ribosome functional?
when 2 subunits come together when mRNA arrives
how many binding sites does mRNA have?
3 binding sites for tRNA - EPA
P site
Peptidyl-tRNA binding site
holds the growing protein
A site
Aminoacyl-tRNA binding site
holds the tRNA bearing the next amino acid
E site
exit site
“empty” tRNA exits from ribosome
what is the function of tRNA?
transfer amino acids from cytoplasm to a ribosome
how many amino acids are within the cytoplasm of the cell?
20
are tRNA molecules identical?
no
laid out, what is the shape of tRNA? natural configuration?
upside down clove leaf, upside down L
anitcodon
segment located on one side of the tRNA which varies
what will the anitcodon bind to?
mRNA’s codons according to the base pairing rules
where do specific amino acids bind to on tRNA?
3’ end
how many tRNA’s are there?
45
why are there 45 tRNA instead of 61?
Wobble Effect - anticodons can recognize 2 or more different codons as 3rd base of codon is not very strict
what does the wobble effect explain?
why synonymous codons for a given amino acids can differ in their 3rd base, but usually not in their other bases
what are the three stages of translation?
initiation, elongation, and termination
what do the stages of translation require?
all three require transcription factors and two need a molecule to energize named GTP (guanine triphosphate)
what does initiation in translation do?
brings together mRNA, tRNA bearing the first amino acid of the polypeptide, and eventually 2 subunits of ribosome
what is the start codon on mRNA?
AUG
what is the anticodon of the start codon on mRNA?
UAC
what bond do the codon and anticodon form?
weak H bond
what does tRNA bring for the start codon?
amino acid methionine
once the start codon is initiated what happens?
the large ribosomal subunit completes the initiation complex, then the tRNA that brought Met is in the P site of the ribosome and is ready to accept the next tRNA bearing an amino acid in the A site
when does the large subunit come in?
only after the first tRNA brings in an amino acid
where does the first tRNA start?
immediately in the P site, not A
what happens in elongation in translation?
next tRNA comes to the A site where its anticodon forms a hydrogen bond with codon of mRNA and a covalent bond forms between the amino acid in the P site and the newly arrives amino acid in the A site
what does the formation of the peptide bond do?
moves the growing polypeptide chain to the newly arrived tRNA, which then causes the tRNA in the P site to translocate to the E site and the tRNA in the A site to the P site and cycle repeats
when does the elongation of the growing polypeptide stop?
until a stop codon (UAA, UAG, UGA) is encountered on mRNA
what happens once a stop codon is encountered?
a protein called release factor frees the polypeptide (the primary level of protein) and the ribosome, mRNA, and tRNA complex breaks apart
how long does the translation process take?
less than a minute
what is a string of ribosomes making proteins called?
polyribosomes
how many ribosomes are translating the same message at the same time?
many
what happens once a polypeptide is made?
it begins to spontaneously fold into secondary and tertiary structures with the aid of chaperonins proteins
after the folding of a polypeptide, what happens next?
other attachments may be made like glycoproteins and lipoproteins
or quaternary structures can be made
what are the two types of ribosome?
free and bound
free ribosome
in cytosol
mostly make proteins that remain in the cytosol and function there
bound ribosome
attached to ER
make proteins of the endomembrane system (nuclear envelope, ER, Golgi, lysosomes, vacuoles, and plasma membrane) and proteins that get secreted from cell
where does translation begin on?
always a free ribosome and the growing peptide may signal the ribosome to attach to the ER
what happens when a ribosome attaches to the ER?
protein usually goes to cisternal space of ER to get folded and eventually secreted
4 types of mutation
Polyploidy - entire set
Nondisjunction - a whole chromosome
Segment of Chromosome
Point
what are point mutations?
mutation that are changes in just one or a few bases
sickle cell anemia
mutation of one base pair that codes for hemoglobin
base pair substitution
replacing 1 nucleotide and its partner with another pair of nucleotides
three types of base pair substitutions
silent
missense
nonsense
silent base pair mutation
codes for the same amino acid
missense base pair mutation
codes for a different amino acid
nonsense base pair mutation
codes for a stop
insertions and deletion mutations
addition or loss of one or more nucleotide pairs
frameshift causing extensive missense
one nucleotide lost or gained changes every amino acid after it
frameshift causing immediate nonsense
one nucleotide lost or gained that codes for a stop
insertion or deletion of 3 nucleotides, no extensive frameshift
loss or gain of one amino acid
mutations caused by an outside/ environmental factors
mutagens
examples of mutagens
physical and chemical agents like plastic, burnt, charred meat, red meat, BPA, cell phone
