Chapter 14 Gene Expression Gene To Protein Flashcards
Proteins are the link between
Genotype and phenotype
Gene Expression
The process by which DNA directs protein synthesis: includes two stages
Transcription
Translation
_______ is the bridge between DNA and protein synthesis
RNA
RNA is similar to DNA but RNA has a ________ sugar and the base ______ rather than thymine
Ribose, uracil
Transcription
The synthesis of RNA using information in DNA
Transcription produces
Messenger RNA mRNA
Translation
Is the synthesis of a polypeptide using information in the mRNA
_________ are the sites of translation
Ribosomes
In _______, translation of _______ can begin before transcription has finished
Bacteria, mRNA
In eukaryotes, the __________separates transcription from translation
Nuclear envelope
Eukaryotic mRNA must be _________ our of the __________ to be translated
Transported, translated
Primary transcript
Is the initial RNA transcript from any gene prior to processing
Central Dogma
Is the concept that cells are governed by a cellular chain of command
The flow of information from gene to protein is based on a
Triplet code- a series of non overlapping three nucleotide words
A chain of amino acids
Polypeptide
During transcription, one of two DNA strands called the ________, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
Template strand
During translation, the mRNA base triplets called, _______ are read in the ________ direction
Codons, 5’ to 3’ direction
Of the 64 triplets, ______code for amino acids_______ triplets are stop signals to end translation
61, 3
The genetic code is _______: more than one codon may specify a particular __________
Redundant, amino acid
No codon specifies more than
One amino acid
Codons must be read in the correct __________
Reading frame
The genetic code is nearly ________, shared by the simplest bacteria and the most complex animals
Universal
_________ is the first stage of gene expressions
Transcription
RNA synthesis is catalyzes by ________ which pries the DNA strands apart and joins together the _________
RNA polymerase, RNA nucleotides
RNA polymerase assembles polynucleotides in the
5’ to 3’ direction
Unlike DNA polymerase, RNA polymerase can
Start a chain without a primer
Promoter
The DNA sequence where RNA polymerase attaches
The sequence signaling the end of transcription is called
The terminator
Transcription Unit
The stretch of DNA that is transcribed
Three stages of transcription
Initiation
Elongation
Termination
________ signal the transcriptional start point
Promoters
Transcription Factors
Mediate the binding of RNA polymerase and the initiation of transcription
As RNA polymerase moves along the DNA, it _______
Untwists the double helix
Transcription progresses at rate of _______ nucleotides per second in eukaryotes
40
Mechanisms of termination for bacteria and eukaryotes
Bacteria- the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification
Eukaryotes- RNA polymerase II transcribes the polydenylation signal sequence
RNA Processing
Enzymes in the eukaryotic nucleus modify pre mRNA before the genetic messages are dispatched to the cytoplasm
Modification of mRNA ends
5’ end receives a modified G nucleotide 5’ cap
The 3’ end gets a poly-A-tail
Introns
The non coding regions are called intervening sequences
Exons
Coded regions of mRNA
RNA Splicing
Removes introns and joins exons creating an mRNA molecule with a continuous coding sequence
Alternative RNA splicing
Genes give rise to two or more different polypeptides depending on which segments are used as exons
RNA splicing is carried out by __________, consisting of ________and _________
Spliceosomes, Proteins, small RNA
Ribozymes
Are RNA molecules that function as enzymes
A cell translates an mRNA message into protein with the help of
Transfer RNA tRNA
TRNA transfer ________ to the growing polypeptide in a ribosome
Amino acids
Each tRNA can translate a particular ______into a given amino acid
mRNA codon
The tRNA contains an ______at one end and at the other end has a ___________ that can base pair with the complementary codon on mRNA
Amino acid, nucleotide triplet
A tRNA molecule consist of a single ________ strand that is about _______ nucleotides long
RNA , 80
tRNA molecules can base pair with
Themselves
Accurate translation requires two steps
First, a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase
Second, a correct match between the tRNA anticodon and an mRNA codon
Flexible pairing at the third base of a codon
Wobble
Wobble allows some tRNA to bind more than one
Codon
A ribosome has three binding sites for tRNA
Psite
A site
Esite
P Site
Holds the tRNA that carries the growing polypeptide chain
A Site
Holds the tRNA that carries the next amino acid to be added to the chain
E Site
Is the exit site where discharged tRNA leave the ribosome
Energy for translation is provided by
GTP
The initiation stage of translation
mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
A small ribosomal subunit binds with mRNA and a special initiator tRNA
Then the small subunit moves along the mRNA until it reaches the start codon
Steps in elongation
Amino acids are added one by one to the previous amino acid at the c-terminus of the growing chain
Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, translocation
Translocation proceeds along the mRNA in a 5’ to 3’ direction
Termination
Occurs when a stop codon in the mRNA reaches the A site of the ribosome
The A site accepts a protein called a release factor
The release factor causes the addition of a water molecule instead of an amino acid
This reaction releases the polypeptide and the translation assembly then comes apart
Two populations of ribosomes in cells
Free ribosomes
Bound ribosomes
Free ribosomes
Mostly synthesize proteins that function in the cytosol
Bound ribosomes
Make proteins of the endomembrane system and proteins that are secreted from the cell
Polypeptide synthesis always begins in the
Cytosol
Synthesis finishes in the _______ unless the polytsignals the ribosome to attach to the _______
Cytosol, ER
Polypeptides destined for the ER or for secretion are marked by a
Signal peptide
Mutations
Changes in the genetic material of a cell or virus
Chemical changes in just one nucleotide pair of a gene
Point mutations
If a point mutation occurs in a gamete it may be transmitted to
Offspring
Two categories of point mutations
Single nucleotide pair substations
Nucleotide pair insertions or deletions
A nucleotide pair substitution
Replaces one nucleotide and its partner with another pair of nucleotides
Silent mutations
Have no effect on the amino acid produced by a codon because of redundancy in the genetic code
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, nearly always leading to a nonfunctional protein
_________ and ______ are additions or losses of nucleotide pairs in a gene
Insertions, deletions
Frameshift mutation
Altering of the reading frame of the genetic message
Mutagens
Physical or chemical agents that can cause mutations
A gene can be defined as
A region of DNA that can be expressed to produce a final functional product, either a polypeptide an RNA molecule
The template strand is always the _______ strand for any given gene.
Same
