Unit 4 lecuture 1 part 2 11/7/22 Flashcards
Enzymes in the _________ modify _________ (RNA processing) before the genetic messages are dispatched to the _________
eukaryotic nucleus
pre-mRNA
cytoplasm
During RNA processing, _________ ends of the primary transcript are altered
both
Also, usually some _________ of the molecule are cut out and the other parts _________
interior parts
spliced together
The _________ receives a modified _________________
5’ end
G nucleotide 5’ cap
The 3′ end gets a _________
Poly A tail
These modifications share several functions:
Facilitating the export of _________ to the _________
Protecting _________ from _________
Helping _________ attach to the _________
mRNA
cytoplasm
mRNA
hydrolytic enzymes
5’ end
Most _________ have long noncoding stretches of nucleotides that lie between coding regions
eukaryotic mRNAs
The noncoding regions are called _________, or _________
intervening sequences
introns
The other regions are called _________ and are usually translated into _________ sequences
exons
amino acids
_________ removes _________ and joins _________, creating an mRNA molecule with a __________________
RNA splicing
introns
exons
continuous coding sequence
Many genes can give rise to _________ different polypeptides, depending on which segments are used as _________
two or more
exons
This process is called __________________, and is carried out by _________
alternative RNA splicing
spliceosome
_________ consist of _________ and small _________
spliceosomes
proteins
RNAs
_________ are RNA molecules that function as enzymes
Ribozymes
RNA splicing can occur _________, or even additional RNA molecules, and introns can catalyze _________
without proteins
their own splicing
A cell _________ an mRNA message into _________ with the help of __________________
translates
protein
transfer RNA(tRNA)
_________ transfer _________ to the growing _________ in a _________
tRNAs
amino acids
polypeptide
ribosome
Each _________ can translate a particular _________ into a given _________
tRNA
mRNA codon
amino acid
The _________ contains an amino acid at one end and at the other end has a _________ that can pair with the _________ on _________
tRNA
nucleotide triplet
complementary codon
mRNA
A _________ molecule consists of a single RNA strand that is only about _________ long
tRNA
80 nucleotides
tRNA molecules can base-pair with _________
themselves
Flattened into one plane, a tRNA molecule looks like a _________
cloverleaf
In three dimensions, _________ is roughly _________, where one end of the L contains the _________ that base-pairs with an mRNA codon
tRNA
L-shaped
anticodon
First: a correct match between a _________ and an _________, done by the enzyme __________________
tRNA
amino acid
aminoacyl-tRNA synthetase
Second: a correct match between the _________ and an _________
tRNA anticodon
mRNA codon
Flexible pairing at the _________ of a codon is called _________ and allows some tRNAs to bind to __________________
3rd base
wobble
more than 1 codon
_________ facilitate specific coupling of _________ with _________ during protein synthesis
Ribosomes
tRNA anticodons
mRNA codons
The large and small ribosomal subunits are made of _________ and __________________
proteins
ribosomal RNAs (rRNAs)
In bacterial and eukaryotic ribosomes the large and small subunits join to form a ribosome only when attached to an _________
mRNA molecule
A ribosome has _________ binding sites for tRNA
3
The _________ holds the tRNA that carries the growing polypeptide chain
P site
The _________ holds the tRNA that carries the next amino acid to be added to the chain
A site
The _________ is the exit site, where discharged tRNAs leave the ribosome
E site
The three stages of translation:
_________
_________
_________
Initiation
Elongation
Termination
All three stages require _________ that aid in the translation process
protein “factors”
The _________ stage of translation brings together _________, a _________ with the first _________, and the two _________
initiation
mRNA
tRNA
amino acid
ribosomal subunits
Then the small subunit moves along the mRNA until it reaches the _________
start codon (AUG)
The _________ is important because it establishes the reading frame for the mRNA
start codon
The addition of the __________________ and completes the formation of the __________________
large ribosomal subunit is last
translation initiation complex
Proteins called _________ bring all these components together
initiation factors
During _________, amino acids are added one by one to the previous amino acid at the _________ of the growing chain
elongation
C-terminus
Each addition involves proteins called _________ and occurs in three steps: _________, _________, and _________
elongation factors
codon recognition
peptide bond formation
translocation
_________ proceeds along the mRNA in a 5′ to 3′ direction
Translation
_________ occurs when a _________ in the _________ reaches the A site of the _________
Termination
stop codon
mRNA
ribosome
The _________ accepts a protein called a _________
A site
release factor
The _________ causes the addition of a _________ instead of an _________
release factor
water molecule
amino acid
This reaction releases the _________, and the translation assembly then comes apart
polypeptide
Two populations of ribosomes are evident in cells: _________ (in the _________) and _________ (attached to the _________)
free ribosomes
cytosol
bound ribosomes
ER
_________ mostly synthesize proteins that function in the _________
Free ribosomes
cytosol
_________ synthesis always begins in the _________
Polypeptide
cytosol
Polypeptides destined for the ER or for secretion are marked by a _________
signal peptide
A __________________ (SRP) binds to the signal peptide
signal recognition particle
Strings of ribosomes called _________ (or polysomes) can be seen with an electron microscope
polyribosomes
In bacteria, the transcription and translation can take _________
place simultaneously
In eukaryotes, the _________ separates transcription and translation
nuclear envelope
_________ are changes in the genetic material of a cell or virus
Mutations
_________ are chemical changes in just one or a few nucleotide pairs of a gene
point mutations
_________ within a gene can be divided into _________ general categories
Point mutations
2
Nucleotide-pair _________
substitutions
One or more nucleotide-pair _________ or _________
insertions
deletions
A nucleotide-pair _________ replaces one nucleotide and its partner with another pair of nucleotides
substitution
_________ have no effect on the amino acid produced by a codon because of redundancy in the genetic code
silent mutations
_________ mutations still code for an amino acid, but not the correct amino acid
Missense
_________ mutations are usually _________ mutations
Substitutions
missense
_________ change an amino acid codon into a stop codon, nearly always leading to a _________ protein
nonsense mutations
nonfunctional
_________ and _________ are additions or losses of nucleotide pairs in a gene
insertions
deletions
These mutations have a disastrous effect on the resulting protein _________ than substitutions do
more often
Insertion or deletion of nucleotides may alter the reading frame of the genetic message, producing a _________
frameshift mutation
_________ are physical or chemical agents that can cause mutations
mutagens
Most cancer-causing chemicals (_________) are mutagenic
carcinogens
