Ch 6 The Control Of Gene Expression

Question 1

Coding RNA

Answer 1

An RNA transcript of a protein-coding gene.

Question 2

Non-coding RNA (ncRNA)

Answer 2

A functional RNA molecule that is not translated into a protein (i.e. the product of a non-coding gene) for example ribosomal RNA (rRNA) or transfer RNA (tRNA).

Question 3

Ribosomal RNA (rRNA)

Answer 3

The RNA that, together with proteins, makes up the structures called ribosomes, which are the sites of synthesis of proteins by the process of translation.

Question 4

Transfer RNA (tRNA)

Answer 4

Small RNA molecules involved in protein synthesis at the ribosome. Each tRNA molecule carries an amino acid and a particular anticodon (a triplet of bases), which binds to a complementary codon in mRNA, adding the appropriate amino acid to the growing polypeptide chain.

Question 5

Primary RNA transcript

Answer 5

A eukaryotic RNA transcript immediately after transcription in the nucleus, before any processing e.g. RNA splicing or polyadenylation.

Question 6

Posttranscriptional modification

Answer 6

The enzymatic processing of the eukaryotic primary RNA transcript to produce a mature transcript; production of a mature mRNA requires capping, polyadenylation and intron splicing.

Question 7

RNA splicing

Answer 7

A post-transcriptional process that removes the non-coding sequences (introns) from the transcribed mRNA to produce the mature mRNA molecule.

Question 8

Post-translational modifications

Answer 8

The enzymatic processing of polypeptides after translation to produce the mature functional protein. For example, proteins that are intended for export, or for incorporation into membranes, pass into the lumen of the ER, where they undergo post-translational modification including glycosylation; the addition of short sugar chains to form a glycoprotein. Other types of modification include the addition of other chemical groups (such as phosphates or lipids) or cleavage.

Question 9

Capping

Answer 9

The process of adding a modified guanosine nucleotide (GTP residue) to the 5’-end (the beginning) of a eukaryotic mRNA molecule.

Question 10

Polyadenylation

Answer 10

The post-transcriptional addition of a series of adenosine nucleotides to the 3’ end of a eukaryotic mRNA.

Question 11

Initiation

Answer 11

Transcription can be divided into three stages. Initiation is the first stage in which the RNA polymerase binds to the DNA template. Translation also has an initiation stage in which a ribosome assembles at the appropriate place on a messenger RNA.

Question 12

Elongation

Answer 12

Transcription can be divided into three stages. Elongation is the second stage (after initiation), in which the RNA polymerase moves along ‘reading’ the DNA template and synthesising RNA. Translation also has an elongation stage.

Question 13

Termination

Answer 13

Transcription can be divided into three stages. Termination is the third stage in which mRNA synthesis (elongation) ceases and the transcript dissociates from the template. Translation also has a termination stage.

Question 14

Core promoter

Answer 14

A region of DNA present in all prokaryotic genes which includes the binding site for RNA polymerase and the site where transcription is initiated.

Question 15

Consensus sequences

Answer 15

The most common sequence of bases (or amino acids) in a region of sequence homology found in many different genes (or proteins) in different species. Conserved sequences often indicate a conserved function.

Question 16

Transcription initiation complex

Answer 16

A complex assembly of proteins, including transcription factors and RNA polymerase, that binds to DNA at a specific site upstream of a gene called a promoter, where it initiates transcription of the gene sequence into RNA.

Question 17

Transcription start site

Answer 17

The site in a gene promoter sequence at which the DNA starts to be copied into RNA sequence during transcription.

Question 18

Regulatory DNA elements

Answer 18

Short consensus sequences in DNA that are specifically recognised and bound by DNA binding proteins called transcription factors. These factors either promote the recruitment of RNA polymerase to the promoter, thereby increasing transcription of the gene (transcriptional activators), or repress recruitment of the RNA polymerase and decrease transcription of the gene (transcriptional repressors).

Question 19

Transcription factors

Answer 19

Proteins that bind to specific DNA sequences, promoting (activators) or inhibiting (repressors) the recruitment of RNA polymerase to specific gene promoters, thereby controlling the transcription of genes.

Question 20

DNA binding motifs

Answer 20

Common structural features on different DNA-binding proteins (includng transcription factors) which facilitate their binding to DNA. Three typical DNA binding motifs are the helix–turn–helix motif, the zinc finger, and the leucine zipper.

Question 21

Catabolite activator protein (CAP)

Answer 21

The gene regulatory protein that binds cAMP and is involved in the transcriptional regulation of some bacterial operons.

Question 22

Lac operon

Answer 22

lac operon - Group of adjacent and coordinately controlled genes concerned with the metabolism of lactose in E. coli.

Question 23

Negative inducible regulation

Answer 23

A type of gene expression control in bacteria. Transcription of a gene under this type of control is induced only when a repressor protein present in the cell is inactivated.

Question 24

Positive inducible regulation

Answer 24

A type of gene expression control in bacteria. Transcription of a gene under this type of control is induced only when an specific activator molecule becomes activated.

Question 25

Attenuation

Answer 25

Describing a mechanism of downregulating gene expression in bacteria, in which the transcription of an mRNA molecule is prematurely terminated due to a structural modification; in other words, the RNA molecule transcribed is incomplete.

Question 26

Transcription terminator

Answer 26

A sequence in RNA being transcribed from a DNA template that, when encountered by the RNA polymerase enzyme, signals the termination of RNA synthesis.

Question 27

Growth factors

Answer 27

A general term for signalling molecules, usually polypeptides, that bind to cells carrying appropriate receptors and ultimately alter gene expression to stimulate growth, survival or division of the cell.

Question 28

Hormones

Answer 28

Signalling molecules that in animals are produced by specialised epithelial cells and transported to their target cells elsewhere in the body via the blood circulation. They affect the growth, behaviour or metabolism of cells with appropriate receptors. Plants also have hormones, referred to as phytohormones. Hormones may be peptides, steroids or other types of molecules.

Question 29

General transcription factors

Answer 29

Proteins that bind to the core promoter and assemble the transcription initiation complex; essential for RNA polymerase binding and the initiation of gene transcription.

Question 30

Specific transcription factors

Answer 30

Molecules that bind to regulatory DNA elements and have an effect on gene expression.

Question 31

Housekeeping genes

Answer 31

Genes that are constitutively expressed (at a relatively constant level) in most cells types in an organism; they code for molecules involved in the basic functions necessary for maintenance of the cell.

Question 32

Enhancers

Answer 32

Regulatory DNA elements which may be located some distance from the gene and, when bound by transcriptional activator proteins, stimulate gene expression. Common in eukaryotes but rare in prokaryotes.

Question 33

Silencers

Answer 33

Regulatory sequences in DNA that, when bound by transcriptional repressor proteins, reduce the rate of transcription of a gene or genes; typically located some distance away from the gene(s). Common in eukaryotes but rare in prokaryotes

Question 34

Northern blotting

Answer 34

A technique used to separate and identify specific cellular mRNA molecules; involving gel electrophoresis and transfer to a synthetic membrane, followed by hybridisation to a labelled probe.

Question 35

Capping

Answer 35

The process of adding a modified guanosine nucleotide to the 5’-end (the beginning) of a eukaryotic mRNA molecule.
Reqd for export through pores nucleus

Ribosome binding and mRNA translation

Prevents enzymes in cytoplasm from degrading mRNA from five prime end before it can be translated

Question 36

Poly(A) tail

Answer 36

The series of adenosine nucleotides added to the 3’ end of eukaryotic mRNA after transcription.

Question 37

MicroRNAs (miRNAs)

Answer 37

Small, non-coding, regulatory RNA molecules, about 22 nucleotides long, found in eukaryotic cells and which can silence the expression of certain genes.

Question 38

Ribosome binding site

Answer 38

A short consensus sequence on mRNA where the ribosome binds during the initiation of translation.

Question 39

Polysomes

Answer 39

The name for the structure formed by a group of ribosomes and partially translated polypeptides attached to a single molecule of mRNA during the process of translation.

Question 40

Combinatorial control

Answer 40

The way a group of transcription factors work together to determine level of expression of a single gene.

Question 41

siRNA

Answer 41

Small interfering RNAs -approximately 22 base pairs long.