Chapter 18

Front 1

Differential Gene Expression

Back 1

Expression of different sets of genes in cells with the same genome. Responsible for creating different cell types.

Front 2

The 6 levels of control of gene expression in eukaryotes

Back 2

1. Chromatin remodelling

2. Transcription

3. RNA processing

4. mRNA stability

5. Translation

6. Posttranslational modification

Front 3

Chromatin

Back 3

The complex of DNA and proteins, mainly histones, that compose eukaryotic chromosomes.

Front 4

Chromatin Remodelling

Back 4

The process by which the DNA in chromatin is unwound from its associated proteins to allow transcription or replication. May involve chemical modification of histone proteins or reshaping of the chromatin by large multi-protein complexes in ATP-requiring process.

Front 5

Nucleosome

Back 5

A repeating, bead-like unit of eukaryotic chromatin, consisting of about 200 nucleotides of DNA wrapped twice around a histone octamer.

Front 6

Histone Octamer

Back 6

A protein complex made up of 8 histone proteins. Used to package eukaryotic DNA into nucleosomes.

Front 7

What are the layers of organization of chromatin in a eukaryotic chromosome?

Back 7

1. The DNA is wrapped around histones to form nucleosomes.

2. Nucleosomes are packed into 30-nm fibres.

3. 30-nm fibres are attached to scaffold proteins.

4. The entire assembly is folded into the highly condensed structure observed in cell division.

Chromatin must decondense for RNA polymerase to bind to the promoter.

Front 8

Acetylation

Back 8

Addition of an acetyl group to a molecule.

Front 9

Methylation

Back 9

The addition of a methyl group to a molecule.

Front 10

Histone Acetyl Transferase (HAT)

Back 10

In eukaryotes, one of a class of enzymes that loosen chromatin structure by adding acetyl groups to histone proteins. On switch for transcription.

Front 11

Histone Deactylase (HDAC)

Back 11

In eukaryotes, one of a class of enzymes that recondense chromatin by removing acetyl groups from histone proteins. Off switch for transcription.

Front 12

Histone Code

Back 12

The hypothesis that specific combinations of chemical modifications of histone proteins contain information that influences gene expression.

Front 13

Epigenetic Inheritance

Back 13

Pattern of inheritance involving differences in phenotype that are not a result of changes in the nucleotide sequence of genes.

Front 14

TATA-Binding Protein (TBP)

Back 14

A protein that binds to the TATA box in eukaryotic promoters and is a component of the basal transcription complex.

Front 15

Regulatory Sequence

Back 15

Any segment of DNA that is involved in controlling transcription of a certain gene by binding certain proteins.

Front 16

Promoter-proximal Elements

Back 16

In eukaryotes, regulatory sequences in DNA that are close to a promoter and that can bind regulatory transcription factors.

Front 17

Enhancer

Back 17

A regulatory sequence in eukaryotic DNA that may be located far from the gene it controls or within introns of the gene. Binding of specific proteins to an enhancer enhances the transcription of certain genes.

Front 18

Silencer

Back 18

A regulatory sequence in eukaryotic DNA to which repressor proteins can bind, inhibiting transcription of certain genes.

Front 19

Regulatory Transcription Factor

Back 19

General term for proteins that bind to DNA regulatory sequences (eukaryotic enhancers, silencers, and promoterproximal elements) but not to the promoter itself, leading to an increase or decrease in transcription of specific genes.

Front 20

Basal Transcription Factor

Back 20

General term for proteins, present in all cell types, that bind to eukaryotic promoters and help initiate transcription.

Front 21

Mediator Complex

Back 21

Regulatory proteins that form a physical link between regulatory transcription factors that are bound to DNA and the basal transcription complex.

Front 22

Steps in how transcription is initiated in eukaryotes

Back 22

1. Regulatory transcription factors bind to DNA and recruit chromatin-remodelling complexes and HATs.

2. The chromatin decondenses and the promoter on DNA is exposed.

3. Proteins are assembled and bind promoter.

4. RNA polymerase II completes the basal transcription complex and transcription begins.

Front 23

Basal Transcription Complex

Back 23

A large multiprotein structure that assembles near the promoter of eukaryotic genes and initiates transcription. Composed of basal transcription factors, TATA binding protein, coactivators, and RNA polymerase.

Front 24

Alternative Splicing

Back 24

In eukaryotes, the splicing of primary RNA transcripts from a single gene in different ways to produce different mature mRNAs and thus different polypeptides.

Front 25

RNA Interference (RNAi)

Back 25

Degradation of an mRNA molecule or inhibition of its translation following its binding by a short RNA (microRNA) whose sequence is complimentary to a portion of the mRNA.

Front 26

Steps in RNA interference

Back 26

1. Transcription of miRNA gene.

2. Precursor miRNA is formed.

3. Mature miRNA formed when enzyme in cytoplasm cuts out hairpin loop.

4. miRNA becomes single stranded and binds to RISC protein complex.

5. miRNA binds to complementary sequence on target mRNA.

6. Enzyme inside RISC cuts mRNA.

Front 27

microRNA (miRNA)

Back 27

A small, single-stranded RNA associated with proteins in an RNA-induced silencing complex. Can bind to complimentary sequences in mRNA molecules, allowing the associated proteins to degrade the bound mRNA or inhibit its translation.

Front 28

RISC

Back 28

RNA-induced silencing complex.

Front 29

Proteasome

Back 29

A multimolecular machine that destroys proteins that have been bound to ubiquitin.

Front 30

Chromatin Remodelling (Bacteria vs. Eukarya)

Back 30

Front 31

Transcription (Bacteria vs. Eukarya)

Back 31

Front 32

mRNA Processing (Bacteria vs. Eukarya)

Back 32

Front 33

mRNA Stability (Bacteria vs. Eukarya)

Back 33

Front 34

Translation(Bacteria vs. Eukarya)

Back 34

Front 35

Posttranslational Modification (Bacteria vs. Eukarya)

Back 35

Front 36

When do mutations lead to cancer?

Back 36

When they affect one of the following classes of genes:

1. Genes that stop or slow the cell cycle

2. Genes that trigger cell growth and division by initiating certain phases in the cell cycle

Front 37

Proto-oncogene

Back 37

Any gene that normally encourages cell division in a regulated manner, typically by triggering specific phases in the cell cycle. Mutation may convert it into an oncogene.

Front 38

Oncogene

Back 38

Any gene whose protein product stimulates cell division at all times and thus promotes cancer development. Often is a mutated form of a gene involved in regulating the cell cycle.