Molecular Biology Chapter 17 Vocabulary

Front 1

Gene expression

Back 1

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

Front 2

Transcription

Back 2

The synthesis of RNA using a DNA
template.

Front 3

Messenger RNA (mRNA)

Back 3

A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies
the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.)

Front 4

Translation

Back 4

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of “language” from nucleotides to amino acids.

Front 5

Ribosomes

Back 5

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See also nucleolus.

Front 6

Primary Transcript

Back 6

An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

Front 7

Triplet Code

Back 7

A genetic information system in which a set of three-nucleotide-long words specify the amino acids for polypeptide chains.

Front 8

Template Strand

Back 8

The DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript.

Front 9

Codons

Back 9

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

Front 10

Reading Frame

Back 10

On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

Front 11

RNA Polymerase

Back 11

An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.

Front 12

RNA Processing

Back 12

Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5' and 3' ends.

Front 13

5' cap

Back 13

A modified form of guanine nucleotide added onto the 5' end of a pre-mRNA molecule.

Front 14

Poly-A tail

Back 14

A sequence of 50–250 adenine nucleotides added onto the 3' end of a pre-mRNA molecule.

Front 15

RNA Splicing

Back 15

After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining
together of the remaining portions (exons).

Front 16

Introns

Back 16

A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA
from which this sequence was transcribed.

Front 17

Exons

Back 17

A sequence within a primary transcript that
remains in the RNA after RNA processing; also
refers to the region of DNA from which this
sequence was transcribed.

Front 18

Spliceosome

Back 18

A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining
the two adjacent exons.

Front 19

Ribozymes

Back 19

An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.

Front 20

Alternative RNA Splicing

Back 20

A type of eukaryotic
gene regulation at the RNA-processing level in
which different mRNA molecules are produced
from the same primary transcript, depending
on which RNA segments are treated as exons
and which as introns.

Front 21

Domains

Back 21

(1) A taxonomic category above the
kingdom level. The three domains are Archaea,
Bacteria, and Eukarya. (2) A discrete structural
and functional region of a protein.

Front 22

Transfer RNA (tRNA)

Back 22

An RNA molecule that
functions as a translator between nucleic acid
and protein languages by carrying specific
amino acids to the ribosome, where they recognize
the appropriate codons in the mRNA.

Front 23

Anticodon

Back 23

A nucleotide triplet at
one end of a tRNA molecule that base-pairs
with a particular complementary codon on an
mRNA molecule.

Front 24

Aminoacyl-tRNA Synthetases

Back 24

An enzyme that joins each amino acid to the appropriate tRNA.

Front 25

P site (peptidyl-tRNA binding site)

Back 25

One of a ribosome’s three binding sites for
tRNA during translation. The P site holds the
tRNA carrying the growing polypeptide chain.
(P stands for peptidyl tRNA.)

Front 26

A site (aminoacyl-tRNA binding site)

Back 26

One of a ribosome’s three binding sites for
tRNA during translation. The A site holds the
tRNA carrying the next amino acid to be added
to the polypeptide chain. (A stands for
aminoacyl tRNA.)

Front 27

E site (exit site)

Back 27

One of a ribosome’s three binding sites for
tRNA during translation. The E site is the place
where discharged tRNAs leave the ribosome.
(E stands for exit.)

Front 28

Polyribosomes (or polysomes)

Back 28

A group of several ribosomes attached
to, and translating, the same messenger RNA
molecule.

Front 29

Signal Peptide

Back 29

A sequence of about 20 amino
acids at or near the leading (amino) end of a
polypeptide that targets it to the endoplasmic
reticulum or other organelles in a eukaryotic cell.

Front 30

Signal-recognition Particle (SRP)

Back 30

A protein-RNA complex that recognizes a signal peptide
as it emerges from a ribosome and helps direct
the ribosome to the endoplasmic reticulum
(ER) by binding to a receptor protein on the ER.

Front 31

Mutations

Back 31

A change in the nucleotide sequence of an organism’s DNA or
in the DNA or RNA of a virus.

Front 32

Point Mutations

Back 32

A change in a single nucleotide pair of a gene.

Front 33

Nucleotide-pair Substitution

Back 33

A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary
strand are replaced by another pair of
nucleotides.

Front 34

Silent Mutation

Back 34

A nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.

Front 35

Missense Mutations

Back 35

A nucleotide-pair substitution that results in a codon that codes for a different amino acid.

Front 36

Nonsense Mutation

Back 36

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

Front 37

Insertions

Back 37

A mutation involving the addition of one or more nucleotide pairs to a gene.

Front 38

Deletions

Back 38

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.

Front 39

Frameshift Mutation

Back 39

A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or
deleted is not a multiple of three, resulting in
the improper grouping of the subsequent
nucleotides into codons.

Front 40

Mutagens

Back 40

A chemical or physical agent that interacts with DNA and can cause a mutation.