Gene to Protein Flashcards
Genes specify ____
proteins
how do genes specify proteins
transcription and translation
transcription
DNA directed synthesis of RNA
eukaryotic cels modify RNA _____ transcription
AFTER
translation
RNA directed synthesis of a polypeptide
what can affect protein structure and function
mutations of one or a few nucleotides
information content of genes
specific nucleotide sequences
DNA inherited by an organism leads to a specific trait by
dictating the synthesis of proteins
the link between genotype and phenotype
proteins
gene expression
process by which DNA directs protein synthesis
two stages in gene expression
transcription and translation
how do genes depict phenotype
through enzymes
one-gene one-enzyme hypothesis
gene dictates production of a specific enzyme
are all proteins enzymes
NO
many proteins are composed of ______ polypeptides with ______
several AND own gene
what did the one-gene one-enzyme hypothesis become
one-gene one-polypeptide
in prokaryotic cells, transcription and translation are
not separated
in eukaryotic cells, where is transcription
nucleus
where is a translation in eukaryotic cells
ribosomes in cytoplasm
how does polymerase add nucleotides
pairing with DNA template
nucleotides are added to the ____ end
3’
sense strand
defined by the promoter
sense strand runs from
5’ to 3’
template strand runs
3’ to 5’
thetemplate strand is also known as
anti-sense strand
transcription produces
mRNA
mRNA is a message to
produce a protein
site of translation
ribosome
why can translation begin before transcription is done in prokaryotes
not separated
what separates transcription from translation in eukaryotes
nuclear enevlope
how are eukaryotic RNA modified to finished mRNA
RNA processing
primary transcript
initial RNA transcript from any gene prior to processing
central dogma
concept that cells are governed by cellular chain of command
what steps are the central dogma
DNA to RNA to PROTEIN
how many nucleotides correspond to an amino acid
3 nucleotides per amino acid
triplet code
series of nonoverlapping, three nucleotide “words”
the flow of information from gene to protein is based on
triplet code
what does the template strand provide
a template for ordering the sequences of complementary nucleotides in RNA transcript
codons
specifies an amino acid placed at the corresponding position along the polypeptide
codons are read in
5’ to 3’
61 of the codons are for
amino acids
3 codons are for
stop signals
start codon
AUG
stop codons
UAA
UAG
UGA
genetic code is
redundant
redundant
more than ONE codon may specify a particular amino acid
the genetic code is not
ambiguous
ambiguous
no codon specifies more than ONE amino acid
what must codons do to specify polypeptides being produced
read in the correct reading frame
reading frame
defined by the start codon and the terminating codon
by being redundant, what does the genetic code prevent
potential mutations by having no change in amino acid despite change in codon
the genetic code is nearly
universal
genes can be what after one species to another
transcribed and translated
first step in gene expression
transcription
three steps in transcription
- initiation
- elongation
- terminantion
initiation
after RNA polymerase binds to the promoter the DNA strand unwinds
what does polymerase do in the initiation
initiates RNA synthesis to the start point on the template strand
direction of polymerase in elongation
downstream
elongation
unwinds the DNA and elongates the RNA transcript 5’ to 3’
termination
RNA transcript is released
what stage does the polymerase detach from the DNA
termination
RNA synthesis is catalyzed by
RNA polymerase
RNA polymerase
separates DNA strands and joins together RNA nucelotides
the sequence of the resulting RNA is complementary to
the DNA template
RNA polymerase does not need
a primer
RNA synthesis follows the same base-pairing rule as
DNA
promoter
DNA sequence where RNA polymerase attaches
in bacteria the sequence signalling the end of transcription is
terminator
transcription unit
stretch of DNA that is transcribed
promoters signal the
transcriptional start point
promoters usually extend
several dozen nucleotide pairs upstream of the start point
transcription factors
mediate binding of RNA polymerase and the initiation of transcripton
transcription-initiation complex
assembly of transcription factors and RNA polymerase II bound to a promoter
TATA box
crucial for forming the initiation complex in eukaryotes
as RNA polymerase moves along DNA it
untwists the double helix
a gene can transcribe simultaneously by
several RNA polymerases
mechanism of termination are _____ in bacteria and eukaryotes
different
in bacteria, the termination
polymerase stops transcription at the end of terminator
in bacteria, the mRNA can be translated
without further modification
in eukaryotes, termination
RNA polymerase II transcribes a polyadenylation signal sequence
pre-mRNA signals that it is what cell
eukaryotic
how do enzymes in the nucleus of eukaryotes modify pre-mRNA
RNA processing
when does RNA processing take place
BEFORE it is released to cyoplasm
during RNA processing both ends of the primary transcript
are altered
primary transcript
pre-mRNA
5’ end of pre-mRNA receives
5’cap of guanine nucleotides
the 3’ end of pre-mRNA receives
poly-A-tail with adenine nucleotides
functions of the alterations of mRNA ends
- facilitate the export of mRNA to the cytoplasm
- protect mRNA from hydrolytic enyzmes
- help ribosomes attach to 5’ end
where do noncoding stretches of nucleotides lie in eukaryotes
between coding regions
noncoding regions are called
intervening sequences or introns
exons
regions that are eventually expressed and translated into amino acids
RNA splicing
removes introns and joins exons
RNA splicing creates
an mRNA molecule with a continuous coding sequence
spliceosomes consist of
variety of proteins and several small nuclear ribonucleoproteins
spliceosomes recognize
splice sites
RNA splicing can be carried out by
spliceosomes
the RNA of spliceosomes does what
catalyze the splicing reaction
ribozymes
catalytic RNA molecules
function of ribozymes
as enzymes
what rendered obsolete the belief that all biological catalysts were proteins
ribozymes
what three properties of RNA enable it to function as an enzyme
- RNA can form a 3D structure
- some bases in RNA contain functional groups
- RNA may hydrogen bond with other nucleic acid
why can RNA form a 3D structure
its ability to base pair with itself
what can some functional groups of RNA do
participate in catalysis
some _____ contain sequences that may regulate gene expression
introns
genes can code _______ polypeptide
more than one
alternative RNA splicing
genes encoding more than one polypeptide depending on which segments are treated as exons during splicing
the number of proteins an organism can produce is _______ than its number of genes
much greater
domains
proteins often have modular architecture consisting of discrete regions
many _____ code for different _____ in a protein
exons AND domains
exon shuffling may result in
the evolution of new proteins
translation is a process where genetic information flows from _____ to _____
mRNA to protein
cell translates mRNA messages into proteins with the help of
tRNA
tRNA
transfer of amino acids to growing polypeptide in a ribosome
molecules of tRNA _____ identical
aren’t
each tRNA molecule carries
a specific amino acid on one end
each tRNA molecule has an
anticodon on the other end
anticodon
base-pairs with a complementary codon on mRNA
what does a tRNA molecule look like
a clover
why can a tRNA molecule fold into a 3D conformation
hydrogen bonds
tRNA has a rough ____ 3D shape
L
what are the two steps needed for accurate translation
- a correct match between a tRNA and amino acid
- correct match between tRNA anticodon and mRNA codon
what catalyzes the match between tRNA and amino acid in translation
aminoacyl-tRNA synthetase
what allows some tRNAs to bind to more than one codon
flexible pairing at the third base of a codon
wobble
flexible pairing at the third base of a codon
what facilitates specific coupling of tRNA anticodons with mRNA condons
ribosomes
what are the two ribosomal units made from
proteins and ribosomal RNA
how many subunits are on a ribosome
two (large and small)
are the ribosomes of bacteria and eukaryotes similar
YES
three binding sites for tRNA in a ribosome
P site
A site
E site
E site of a ribosome is the
exit site
p site of a ribosome is the
peptidyl-tRNA biding site
A site of a ribosome is the
aminoacyl-tRNA binding site
three stages of translation
initiation, elongation, terminantion
what do all three stages of translation require
protein “factors” that aid in the translation process
do some steps in translation require energy
YES
what does initiation bring together in translation
mRNA, tRNA with the first amino acid and two ribosomal subunits
what happens to the small ribosomal subunit in initiation during translation
binds with mRNA and a special initiator tRNA and moves along the mRNA until reaching the start codon
initiation factors in translation
proteins that bring in the large subunit that completes the translation initiation complex
what completes the translation initiation complex
the arrival of a large ribosomal subunit
what happens during the elongation of translation
amino acids are added one by one to the preceding amino acid
where are amino acids added during the elongation of translation
at the C terminus of the growing chain
what does each addition of amino acids require in translation
elongation factors
elongation factors occur in three steps
- codon recognition
- peptide bond formation
- translocation
what direction does translation proceed along the mRNA
5’ to 3’
what steps are the energy used in translation
1st (codon recognition) and 3rd (translocation) steps
when does termination occur in translation
when a stop codon in the mRNA reaches the A site of the ribosome
what does the site accept in translation termination
release factor
release factor causes
the addition of WATER molecule instead of an amino acid
what releases the polypeptide and causes the translation assembly to come apart
the addition of water instead of an amino acid (release factor)
is translation sufficient to make a functional protein
NO
what happens to polypeptide chains after translation
- modified
- targeted to a specific site in the cell
what does a polypeptide do during and after synthesis
begins to coil and foil into its 3D shape
what dictates primary structure
gene
what does primary structure dictate
shape
what might be needed for proteins to be fully functional
post-translation modifications
two populations of ribosomes in cells
free and bound ribosomes
free ribosomes are in the
cytosol
bound ribosomes are
attached to the ER
free ribosomes synthesize
proteins that function in the cytosol
bound ribosomes make
proteins of the endomembrane system and those secreted by the cell
ribosomes are _______
identical
because ribosomes are identical they can do what
switch from free to bound ribosomes
where does polypeptide synthesis begin
in the cytosol
synthesis of a polypeptide will finish in the _____ UNLESS a polypeptide signals ribosome to _______
cytosol OR attach to ER
what are polypeptides destined for ER or secretion marked by
signal peptide at amino terminus
signal-recognition particle
binds to the signal peptide and brings it and its ribosome to the ER
polyribosome or polysome
multiple ribosomes can translate a single mRNA simultaneously
what does forming a polysome enable cells to do
make many polypeptides very quickly
how do bacteria ensure a streamlined process
coupling transcription and translation
with bacteria, the newly made protein can
quickly diffuse to its site of function
with eukaryotes what separates transcription and translation
nuclear envelope
mutations
changes in the genetic material of a cell or virus
point mutations
changes in just ONE base pair of a gene
what mutation can lead to the production of an abnormal protein
point mutation
a genetic disorder or hereditary disease
mutation has effect on the phenotype of the organism
two categories of point mutations
- nucelotide-pair substitutions
- one or more nucleotide-pair insertions or deletions
nucleotide-pair substitution
replaces one nucleotide and its partner with another pair of nucelotides
what are three possible outcomes from a nucleotide-pair substitution
- silent mutation
- missense mutation
- nonsense mutation
silent mutation
no effect on amino acid produced by codon
why do silent mutations have no effect on amino acid
genetic code redundancy
missense mutations
still code for an amino acid but not the correct amino acid
nonsense mutations
change an amino acid codon into a stop codon
what does a nonsense mutation lead to
nonfunctional protein
insertions and deletions are the ______ in a gene
additions or losses of nucleotide pairs
what mutations have disastrous effects on the protein more often than substitutions
insertions and deletions
what can insertions or deletions alter
the reading frame
what can produce a frameshift mutation
insertion or deletion
when can spontaneous mutations occur
during DNA replication, recombination or repair
mutagens
physical or chemical agents that cause mutations
what have we considered a gene as
- discrete unit of inheritance
- specific nucleotide sequence in a chromosome
- DNA sequence that codes for specific polypeptide chain
