F215 1.1 - Cellular Control

Question 1

Addition

Answer 1

Sometimes called insertion. A gene mutation where one of more nucleotides are added.

Question 2

Apoptosis

Answer 2

An orderly process of programmed cell death whereby a cell can dismantle itself in a way that does not damage other cells should circumstances demand it e.g. if infected by pathogens or if there is irreversible DNA damage.

Question 3

Bleb

Answer 3

An irregular bulge in the plasma membrane of a cell, caused by localized decoupling of the cytoskeleton from the plasma membrane. Blebs form during apoptosis.

Question 4

Cistron

Answer 4

A length of DNA encoding a polypeptide usually in prokaryotes where an operon contains several cistrons one after the other, all being transcribed into a single polycistronic mRNA.

Question 5

Cyclic AMP

Answer 5

Cyclic or cAMP is a secondary messenger, used for intracellular signal transduction, such as transferring into cells the effects of hormones like glucagon and adrenaline, which cannot pass through the cell membrane.

Question 6

Deletion

Answer 6

A gene mutation where one of more nucleotides are deleted.

Question 7

Exons

Answer 7

The base-sequences of mRNA which are joined together after the introns have been removed to form the final mRNA for translation.

Question 8

Gene mutation

Answer 8

Also called a point mutation. A change in the base sequence in a gene. Mutations can be neutral, beneficial or harmful.

Question 9

Genetic code

Answer 9

The correlation between the sequences of nucleotides in the coding strand of DNA and the sequences of amino acids in a polypeptide whereby each successive set of three DNA bases guides the insertion of the next amino acid e.g. TTT in DNA will direct insertion of phenylalanine in the protein.

Question 10

Hox genes

Answer 10

A set of genes which direct the development of body segments i.e. they act as master control genes which influence the expression of batteries of other genes by encoding regulatory proteins able to bind to DNA.

Question 11

Hox cluster

Answer 11

A collection of Hox genes.

Question 12

Inducer

Answer 12

A molecule which switches on the expression of an operon in a prokaryote by binding to a repressor protein so that the latter no longer obstructs the passage of RNA polymerase along the DNA e.g. lactose induces expression of the genes of the lac operon.

Question 13

Intron

Answer 13

A nucleotide sequence in mRNA which is removed before the mRNA is translated. Intron removal is called post-transcriptional modification.

Question 14

Messenger RNA

Answer 14

Also called mRNA. The type of RNA that transfers the sequence information from the DNA to the ribosome where it is translated into the corresponding polypeptide sequence.

Question 15

Necrosis

Answer 15

Unprogrammed cell death (different to apoptosis) leading to release of toxic chemicals and death of adjacent cells.

Question 16

Operator

Answer 16

A sequence of nucleotides in DNA in prokaryotes, located at the start of an operon, to which a repressor protein can bind thus obstructing the binding/movement of RNA polymerase and therefore preventing production of mRNA and therefore of protein not needed by the cell at that time.

Question 17

Operon

Answer 17

A collection of genes of related function e.g. the enzymes of a single metabolic pathway, located sequentially on a chromosome and all controlled as a unit from a single operator.

Question 18

Polycistronic

Answer 18

Used to refer to an mRNA molecule which contains the coding sequences for a series of proteins of related functions all transcribed from a single operon. These will be translated in turn by a ribosome moving along the message to give separate proteins.

Question 19

Promotor

Answer 19

The sequence of nucleotides on DNA at the start of a gene or operon to which RNA polymerase binds and where transcription of mRNA, rRNA or tRNA begins.

Question 20

Repressor

Answer 20

A protein encoded by a regulatory gene which recognises and binds to a specific sequence of nucleotides in DNA preceding the first structural gene of an operon thus preventing transcription of the operon. It can be made to fall off in the presence of an inducer which binds to it, causing a conformational change so it can no longer recognise the relevant DNA sequence.

Question 21

Ribosomal RNA

Answer 21

Also called rRNA. The type of RNA that makes up about half the mass of each ribosomal subunit

Question 22

Ribosome

Answer 22

The cellular organelle responsible for translating the nucleotide sequence of mRNA into the primary structure of a polypeptide. 2 types exist; small or 70S in prokaryotes, mitochondria and chloroplasts, and large or 80S in eukaryotic cytoplasm, either free or bound to rough endoplasmic reticulum.

Question 23

Substitution

Answer 23

A gene mutation where one of more nucleotides are replaced by different nucleotides

Question 24

Transcription

Answer 24

The formation of mRNA alongside DNA

Question 25

Transcription factor

Answer 25

A protein which regulates the transcription of a gene

Question 26

Transfer RNA

Answer 26

Also called tRNA. The type of RNA responsible for bringing the appropriate amino acid to the ribosome for insertion into a growing polypeptide chain. An anticodon on the tRNA hydrogen bonds to the specific, complementary codon on the mRNA and an enzyme on the ribosome catalyses peptide bond formation.

Question 27

Translation

Answer 27

The synthesis of a specific polypeptide on a ribosome using the base-coding sequence in an mRNA, tRNA, amino acids and enzymes.

Question 28

Triplet

Answer 28

A set of 3 bases in DNA or RNA. The genetic code is called a triplet code as 3 bases code for one amino acid.