Chapter 13: Gene Structure and Expression

Question 1

Polypeptide

Answer 1

The linking of appropriate amino acids

Question 2

Transcription

Answer 2

The first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase.

Question 3

Translation

Answer 3

Occurs in the cytosol. Ribosomes read
the nucleotide code
of the mRNA and make a polypeptide by linking together the appropriate amino acids. The ribosome reads the mRNA in three base chunks called codons and translates the code into a protein using specific tRNAs. The Stages are initiation→elongation→termination.

Question 4

Messenger RNA (mRNA)

Answer 4

A mobile copy of a gene made during transcription.

Question 5

What does the ribosome do?

Answer 5

Reads 
the nucleotide code 
of the mRNA and makes a polypeptide by linking together the appropriate amino acids. It reads the mRNA in three base chunks called codons and translates the code into a protein using specific tRNAs.

Question 6

Genetic Code

Answer 6

What is translated by the tRNA.

Question 7

Codon

Answer 7

The 3 base chaunks that the ribosome reads the mRNA in before translating them into a protein using tRNAs.

Question 8

tRNA

Answer 8

The transfer interpeters. They translate a code into a protein.

Question 9

Start/Initiator codons

Answer 9

The first codon of a messenger RNA (mRNA) transcript translated by a ribosome.

Question 10

Stop (nonsense/termination) codons.

Answer 10

The first codon of a messenger RNA (mRNA) transcript translated by a ribosome.

Question 11

RNA polymerase

Answer 11

Opens the DNA double helix and begins to move along the DNA strand, making a mobile copy” of the gene, called an mRNA or messenger-RNA.

Question 12

Promoter

Answer 12

Binds the RNA polymerase and signals the start of the gene.

Question 13

TATA box

Answer 13

A sequence found in the promoter that signals where transcription will start.

Question 14

Transcription unit

Answer 14

Contains the information required to direct translation of the amino acid sequence.

Question 15

Transcription stop point

Answer 15

Marks the ends of he gene and signals the end of transcription.

Question 16

Transcription factor

Answer 16

They recognize the promoter region of the gene and direct the interaction of the RNA polymerase with the DNA strand.

Question 17

Terminators

Answer 17

A stop codon terminates transcription.

Question 18

Precursor-mRNA (pre-mRNA)

Answer 18

An immature single strand of messenger ribonucleic acid (mRNA). Pre-mRNA is synthesized from a DNA template in the cell nucleus by transcription.

Question 19

5’ cap

Answer 19

Required for export of the mRNA from the nucleus and for binding of the mRNA to the ribosome so translation can occur.

Question 20

Polyadenylation

Answer 20

The addition of a poly(A) tail to a messenger RNA. The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature messenger RNA (mRNA) for translation.

Question 21

Poly(A) tail

Answer 21

A stretch of RNA that has only adenine bases.

Question 22

Intron

Answer 22

Sequences of DNA that are transcribed but are removed before translation.

Question 23

Exon

Answer 23

Expressed sequences which are stuck to ether to give the translatable sequence.

Question 24

mRNA splicing

Answer 24

A modification of the nascent pre-messenger RNA (pre-mRNA) transcript in which introns are removed and exons are joined. For nuclear encoded genes, splicing takes place within the nucleus after or concurrently with transcription.

Question 25

Initiation

Answer 25

For Translation to begin, the small subunit binds to the

mRNA.

Question 26

Elongation

Answer 26

During elongation, a new tRNA enters the A-site. The tRNA will match the codon of the mRNA.

Question 27

Termination

Answer 27

Encoded by the genetic code, a stop codon will tell the ribosome when to finish translation of a given polypeptide. Rather than a stop tRNA a release factor will bind in the A-site
of the ribosome.

Question 28

Anticodon

Answer 28

The complementary sequence to that of the genetic code.

Question 29

Ribonucleoprotein

Answer 29

A nucleoprotein that contains RNA, i.e. it is an association that combines ribonucleic acid and protein together (referred also as protein-RNA complexes).

Question 30

Ribosomal RNA

Answer 30

The RNA component of the ribosome, and is essential for protein synthesis in all living organisms.

Question 31

Ribosomal Sites (3)

Answer 31

1. A (aminoacyl) site
2. P (peptidyl) site
3. E (exit) site

Question 32

A (aminoacyl) site

Answer 32

The binding site for the aminoacyl-tRNA on ribosomes.

Question 33

P (peptidyl) site

Answer 33

One of two tRNA binding sites on a ribosome that holds the tRNA that is normally linked to the polypeptide chain.

Question 34

E (exit) site

Answer 34

Site on the ribosome through which tRNAs pass after they have donated their amino acid to the growing nascent polypeptide chain.

Question 35

Initiator tRNA

Answer 35

A special type of transfer ribonucleic acid (RNA) that initiates protein synthesis by binding to the amino acid methionine and delivering it to the small ribosomal subunit.

Question 36

Ribosome binding site

Answer 36

An RNA sequence found in mRNA to which ribosomes can bind and initiate translation.

Question 37

Peptidyl-tRNA

Answer 37

Formed in the ribosome, it is the tRNA carrying the growing peptide chain.

Question 38

Peptidyl transferase

Answer 38

The primary enzymatic function of the ribosome, which forms peptide bonds between adjacent amino acids using tRNAs during the translation process of protein biosynthesis.

Question 39

Release factor

Answer 39

Binds in the A site of the ribosome to stop translation.

Question 40

Polysome

Answer 40

A cluster of ribosomes held together by a strand of messenger RNA that each ribosome is translating.

Question 41

Signal Peptide

Answer 41

A short peptide present at the N-terminus of the majority of newly synthesized proteins that are destined towards the secretory pathway.

Question 42

Mutation

Answer 42

The changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.

Question 43

Base-pair substitution

Answer 43

A type of mutation involving replacement or substitution of a single nucleotide base with another in DNA or RNA molecule.

Question 44

Missense mutation

Answer 44

When the change of a single base pair causes the substitution of a different amino acid in the resulting protein. This amino acid substitution may have no effect, or it may render the protein nonfunctional.

Question 45

Nonsense mutation

Answer 45

A mutation in which a sense codon that corresponds to one of the twenty amino acids specified by the genetic code is changed to a chain-terminating codon.

Question 46

Silent mutation

Answer 46

DNA mutations that do not significantly alter the phenotype of the organism in which they occur. Silent mutations can occur in non-coding regions (outside of genes within introns), or they may occur within exons.

Question 47

Frameshift mutation

Answer 47

A genetic mutation caused by indels (insertions or deletions) of a number of nucleotides in a DNA sequence that is not divisible by three.