Molecular Biology Chapter 18 Outline

Front 1

Prokaryote Gene Regulation

Back 1

A. Operator
B. Operon

Front 2

Operator

Back 2

Sequence of nucleotides near the start of an operon to which an active repressor can
attach (on-off switch).
1. Repressor prevents RNA polymerase from attaching to promoter and transcribing genes.

Front 3

Operon

Back 3

Unit of genetic function consisting of a promoter, an operator, and a regulated cluster of
genes (regulator gene) whose products function in a common pathway.

Front 4

Promoter

Back 4

Stretch of DNA to which RNA polymerase attaches and initiates transcription.

Front 5

Repressor

Back 5

Protein that inhibits gene transcription (the “off” switch; operon is normally in the “on” position).
a) Blocks attachment of RNA polymerase, preventing transcription; operon specific.

Front 6

Regulatory gene

Back 6

Gene that codes for a protein (repressor) that controls the transcription of another gene or a group of genes.

Front 7

Corepressor

Back 7

Small molecule that binds to a bacterial repressor protein and changes the protein’s shape, allowing it to bind to the operator and switch an operon off.

Front 8

Inducer

Back 8

Small molecule that binds to a bacterial repressor protein and changes the protein’s shape, preventing it from binding to the operator and switching an operon on.

Front 9

repressor protein

Back 9

Regulation of both the trp and lac operons involves the negative control of genes – the
operons are switched off by the active form of the repressor protein.

Front 10

Cyclic AMP (cAMP)

Back 10

Regulator of some bacterial operons; derived from ATP. Common intracellular signaling molecule in eukaryotic cells (second messenger).

Front 11

Activator

Back 11

Protein that binds to DNA and stimulates gene transcription; binds in or near the promoter.
a) Catabolic Activator Protein (CAP).

Front 12

Differential Gene Expression

Back 12

Expression of different sets
of genes by cells with the same genome.
1. Transcription is a common point for gene expression.
2.Extracellular signals initiate gene regulation (hormones).

Front 13

Histone Modification

Back 13

a) Chemical modifications to histones play direct role in the regulation of gene transcription.

Front 14

Histone

Back 14

Small protein with a high proportion of positively charged amino acids that binds to negatively charged DNA; plays a key role in chromatin structure.

Front 15

Histone acetylation

Back 15

Attachment of acetyl groups to certain amino acids of histone proteins; chromatin becomes less compact and the DNA is accessible for transcription.

Front 16

DNA methylation

Back 16

Presence/adding of methyl groups on DNA bases (usually C).
i) Long stretches of inactive DNA (for instance, second X chromosome) and genes in cells that are not expressed are more methylated.

Front 17

Genomic imprinting

Back 17

Methylation pattern which permanently regulates expression of either the maternal or paternal alleles of particular genes at the start of development.

Front 18

Epigenetic Inheritance

Back 18

Inheritance of traits transmitted by mechanisms not directly involving nucleotide sequences of a genome.
a) May explain differences in twins.
b) Epigenetic code offers genome flexibility.
c) Reversible.

Front 19

Control element

Back 19

Segment of noncoding DNA that helps regulate transcription of a gene by serving as a binding site for a transcription factor.
a) Transcription factors regulate transcription.
b) Critical to precise regulation of gene expression

Front 20

Transcription factor

Back 20

Regulatory protein that binds to DNA and affects transcription of specific genes.

Front 21

Enhancer

Back 21

Segment of DNA containing multiple control elements, usually located far from the gene whose transcription it regulates.

Front 22

Alternative RNA splicing

Back 22

mRNA molecules are produced from the same primary transcript, de-pending on which RNA segments are treated as exons or introns.

Front 23

mRNA Degradation

Back 23

a) Lifespan of mRNA in cytoplasm is important in determining pattern of protein synthesis.
b) Bacterial mRNA molecules are degraded by enzymes within a few minutes of their synthesis. Quickly change patterns of protein synthesis in response to environmental changes
c) mRNA molecules in multicellular eukaryotes typically survive for hours, days, or even weeks.
d) mRNA for hemoglobin in developing RBC’s are unusually stable, long-lived, and repeatedly used.

Front 24

Initiation of Translation

Back 24

In some mRNA’s, translation can be blocked by regulatory proteins binding to specific sequences or structures of the mRNA preventing the attachment of ribosomes.- In eggs of many organisms, stored mRNA’s lack poly-A tails long enough to allow translation initiation – during embryonic development, more A’s get added prompting translation to begin.

Front 25

Protein Processing and Degradation

Back 25

Final opportunities for controlling gene expression occur after translation:
i. Process proteins for functional protein molecules.
ii. Add phosphate groups to in/activate proteins.
iii. Add sugars to in/activate cell surface proteins
iv. Transport proteins to target destinations in order to function.

Front 26

proteasomes

Back 26

Giant protein complex that recognizes and destroys proteins tagged for elimination by the smaller protein ubiquitin
i. Regulates the length of time each protein functions.
ii. Example: cyclins during cell cycle = short-lived.

Front 27

Non-coding RNA’s

Back 27

Protein-coding DNA accounts for only 1.5% of the human genome. -Small
percent of the non-protein-coding DNA consists of genes for RNA’s (rRNA, tRNA). -Significant part of the genome may be transcribed into non-protein-coding RNA’s (non-coding or ncRNA’s).

Front 28

microRNA’s (miRNA’s)

Back 28

Small single-stranded RNA molecule that associates with one or more proteins in a complex that can degrade or pre-vent mRNA translation with a complementary sequence.
a) Up to 1/2 of all human genes may be regulated by miRNA’s.

Front 29

dicer

Back 29

Enzyme that trims the precursor mRNA into a double-stranded fragment about 22 nucleotides in length.

Front 30

small interfering RNA’s (siRNA’s)

Back 30

Associated with one or more proteins in a complex that can degrade or prevent translation of an mRNA with a complementary sequence.
a) Produced from same cellular machinery as miRNA’s.
b) Can also block transcription by promoting chromatin modification.

Front 31

Cell differentiation

Back 31

Process by which cells become specialized in structure and function.

Front 32

Morphogenesis

Back 32

Physical processes that give an organism its shape.

Front 33

Cytoplasmic determinants

Back 33

Maternal substance such as protein or RNA that when placed into an egg, influences the course of early development.
a) Regulates expression of genes that affect the developmental fate of cells.

Front 34

Induction

Back 34

Process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression.
a) Contact made by cell-surface molecules and binding of growth factors secreted by
neighboring cells.

Front 35

Determination

Back 35

Progressive restriction of developmental potential in which the possible fate of each cell becomes more limited as an embryo develops.
a) At end of determination a cell is committed to its fate in order for tissues to function properly.

Front 36

Pattern formation

Back 36

Development of a multicellular organism’s spatial organization; arrangement of tissues and organs in their characteristic places.

Front 37

Positional information

Back 37

Molecular cues that control pattern formation in an animal/plant embryonic structure by indicating a cell’s location relative to the body’s axes.

Front 38

Types of Genes Associated with Cancer

Back 38

Mutations that alter genes which regulate growth factors, receptors, and signaling intracellular molecules may result in cancer.
1. Spontaneous mutations may lead to cancer.
2. Environmental influences may lead to cancer.
Chemical carcinogens, High-energy radiation,
Viruses.

Front 39

Oncogene

Back 39

Gene found in viral or cellular genomes that are involved in triggering molecular event that can lead to cancer.

Front 40

Proto-oncogene

Back 40

Normal cellular gene that has the potential to become an oncogene.

Front 41

Tumor-suppressor gene

Back 41

Gene whose protein product inhibits cell division, thereby prevent-ing uncontrolled growth that contributes to cancer.

Front 42

p53 gene

Back 42

Tumor-suppressor gene that codes for a specific transcription factor that pro-motes the synthesis of proteins that inhibits the cell cycle.
a) Functions as an activator for other genes.
i. p21 – halts cell cycle allowing for DNA repair.
ii. miRNA’s which also halt the cell cycle.
iii. Genes directly involved in DNA repair.
iv. Suicide genes if DNA is irreparable

Front 43

Multistep Model of Cancer Development

Back 43

1. More than one mutation needed to produce changes to generate cancer cells.
2. With age, mutations increase as does the incidence of cancer.
3. Usually requires the presence of at least one active oncogene and the mutation or loss of several tumor-suppressor genes