Bio 210 Chapter 17 From Gene to Protein

Elongation of the RNA strand

As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time Transcription progresses at a rate of 40 nucleotides per second in eukaryotes A gene can be transcribed simultaneously by several RNA polymerases Nucleotides are added to the 3′ end of the growing RNA molecule

molecular components of translation

Transfer RNA (tRNA) and ribosomes

stop codon

UAG, UAA, or UGA; the codon that ends all RNA.

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

Codons

mRNA base triplets.

gene expression

process by which a gene produces its product and the product carries out its function

three stages of transciption

initiation, elongation, termination

termination of translation

- occurs when the codon in A-site is a stop codon - release factor places a water molecule on the polypeptide chain and thus releases the protein

Elongation of the Polypeptide Chain

-During the elongation stage, amino acids are added one by one to the preceding 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, and translocation -Translation proceeds along the mRNA in a 5′ to 3′ direction

initiation factors

A class of proteins that assist ribosomes in binding to a messenger RNA molecule to begin translation.

transcription unit

A region of DNA that is transcribed into an RNA molecule.

Three sites of the ribosome

A site, P site, E site

Structure of tRNA

A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long Because of hydrogen bonds, tRNA actually twists and folds into a three-dimensional L-shaped molecule Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf

messenger RNA (mRNA)

A type of RNA, synthesized from DNA and attached to ribosomes in the cytoplasm; it specifies the primary structure of a protein.

Which of the following is not true of a codon? A) It extends from one end of a tRNA molecule. B) It consists of three nucleotides. C) It is the basic unit of the genetic code. D) It may code for the same amino acid as another codon. E) It never codes for more than one amino acid.

A) It extends from one end of a tRNA molecule.

The template strand of a given gene includes the sequence 3¢-G C C A C G T A T C A G-5¢. What is the sequence of the nontemplate strand?

A.5¢-C G G T G C A T A G T C-3¢

Transfer RNA (tRNA)

An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA

Which of the following is the best example of gene expression? A) A frog adapts to variation in its environmental temperature. B) Mouse fur color results from pigment formed by gene-encoded enzymes. C) DNA is replicated during the S phase of the cell cycle. D) The percent of A versus a alleles in a population is altered by natural selection. E) Mutation alters the sequence of a region of DNA.

B) Mouse fur color results from pigment formed by gene-encoded enzymes.

Which of the following components doesn't form part of the transcription complex at a eukaryotic promoter? A. TATA box B. start point C. transfer RNA D. transcription factors E. RNA polymerase

C) transfer RNA

Transcription factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

Which of the following can be the final product of an expressed protein-coding gene? A. mRNA B. tRNA C. rRNA D. polypeptide

D) polypeptide

Central Dogma

DNA -> RNA -> Protein

Which of the following is not a modification made to eukaryotic mRNA before it goes to the cytosol? A.The 5¢ end is capped B.A poly-A tail is added to the 3¢ end C.Introns are removed D.Exons are joined together E.Splice ribosomes are removed

E) Splice ribosomes are removed

RNA polymerase

Enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription

Which of the following terms does not pertain to translation? A. anticodon B. tRNA C. aminoacyl-tRNA synthetase D. polypeptide E. rRNA F. DNA

F) DNA

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

wobble

Flexibility in the base-pairing rules in which the nucleotide at the 5' end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position of a codon.

terminator

In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

RNA processing in eukaryotes

Occurs in nucleus. After transcription: 1.) Capping on 5' end (7-methylguanosine) 2.) Polyadenylation on 3' end (~200 A's) 3.) Splicing out of introns Only processed RNA is transported out of the nucleus.

start codon (AUG)

On mRNA, the specific three-nucleotide sequence (AUG) to which an initiator tRNA molecule binds, starting translation of genetic information.

Translation

Process by which mRNA is decoded and a protein is produced

RNA splicing

Process by which the introns are removed from RNA transcripts and the remaining exons are joined together.

release factor

Proteins that can trigger termination of RNA translation when a ribosome reaches a stop codon.

Which of the following is not a difference between prokaryotic and eukaryotic transcription?

RNA polymerase requires a primer in bacteria; in eukaryotes, it does not.

initiator tRNA

Special tRNA that initiates the translation of an mRNA in a ribosome. It always carries the amino acid methionine.

Template strand

The DNA strand that provides the template for ordering the sequence of nucleotides in an mRNA transcript.

Transcription initiation complex

The completed assembly of transcription factors and RNA polymerase bound to a promoter.

primary transcript

The initial mRNA transcript that is transcribed from a protein coding gene. Also called pre-mRNA.

RNA processing

The modification of mRNA before it leaves the nucleus that is unique to eukaryotes.

Ribosomes function

bring mRNA and tRNA together for protein synthesis

initiation stage of translation

brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits

Extrons

expressed sequence of DNA; codes for a protein

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon

Aminoacyl-tRNA synthetase is an enzyme whose function is to ________.

link a tRNA to its amino acid

termination of transcription in eukaryotes

polymerase continues transcription after the pre-mRNA is cleaved from the growing RNA chain; the polymerase eventually falls off the DNA

Termination of Transcription in bacteria

polymerase stops transcription at the end of the terminator

three stages of translation require

protein "factors" that aid in the translation process

Introns

sequence of DNA that is not involved in coding for a protein

Ribosomes

site of protein synthesis

Promoter

specific region of a gene where RNA polymerase can bind and begin transcription

Transcription

synthesis of an RNA molecule from a DNA template

E site

the exit site, where discharged tRNAs leave the ribosome

The ability of genes from one species to be expressed in a different species is possible because of which property of the genetic code?

the near universality of the genetic code

In eukaryotic cells, transcription cannot begin until

the two DNA strands have completely separated and exposed the promoter.

translation initiation complex

the union of mRNA, initiator tRNA, a small ribosomal subunit, and a large ribosomal subunit

Ribosomal RNA (rRNA)

type of RNA that makes up the major part of ribosomes