Bio II - Chp. 13

Do bacteria require the same enzymes all the time?

No

Who proposed the operon model

Jacob and Monod in 1961

Operon

Group of structural and regulatory genes that function as a single unit

What are the components of an operon

Promoter, operator, structural genes, and a regulatory gene

Promoter

Short segment of DNA where RNA polymerase first attaches

Operator

Short segment of dna where active repressive binds

Structural genes

One to several genes coding for enzymes of a metabolic pathway, transcribed simultaneously as a block

Regulatory gene

Codes for a repressor protein that controls the operon, normally located outside the operon and is controlled by depressor proteins

What happens if there is no tryptophan present

The repressor is unable to attach to the operator, rna polymerase binds to the promoter, enzymes for the synthesis of tryptophan are produced

What happens if tryptophan is present

It combines with the repressor as its corepressor, repressor becomes functional when bound to tryptophan, repressor blocks synthesis of enzymes in the pathway for tryptophan synthesis

The _________ codes for a repressor

Regulator

What happens if lactose is absent

The repressor attaches to the operator, the expression is "off"

What happens if lactose is present

It combines with the repressor and renders it unable to bind to the operator, rna polymerase binds to the promoter, the three enzymes necessary for lactose catabolism are produced

Does E. coli prefer glucose or lactose

Glucose

The lac operon is maximally activated only in the ___________ of glucose

Absence

What occurs when glucose is absent

cAMP (cyclic AMP) accumulates and binds to CAP (catabolic activator protein). CAP, when bound to CAMP, binds to a site near the lac promoter. When CAP is bound, rna polymerase binds better to the promoter. The structural genes of the lac operon are expressed more efficiently

What occurs when glucose is present

There is little CAMP in the cell, CAP is inactive, the lac operon is not expressed maximally

Are operons associated with eukaryotic gene expression or prokaryotic gene expression

Prokaryotic gene expression

In eukaryotic gene expression, what are the five primary levels of control

Nuclear levels: chromatin structure, transcriptional control, posttranscriptional control

Cytoplasmic levels: translational control, posttranslational control

Eukaryotic dna is associated with ________ proteins

Histone

Histone proteins make up __________

Chromatin

Describe nucleosomes

Dna wound around groups of eight molecules of Histone proteins, looks like beads on a string, each bead is called a nucleosome

What determines the level of chromatin packing

The degree of nucleosome coiling

Describe euchromatin structure

Loosely coiled dna, transcriptionally active

Describe heterochromatin structure

Tightly packed dna, transcriptionally inactive

Barr body

The inactive X chromosome

Do females have one active and one inactive X chromosome

Yes

Describe the structure of a Barr body chromosome

Tightly packed along its entire length

What controls transcription

Proteins called transcription factors

Transcription factors

Proteins that help regulate transcription by assisting the binding of the rna polymerase to the promoter

Transcriptional activator

Dna binding protein that binds to enhancer dna

Enhancer DNA

Regions of dna where factors that regulate transcription can also bind

Are transcription factors always present in the cell

Yes

Where does posttransitional control operate

The primary mRNA transcript

What does postranscriptional control determine

Excision of introns, polyadentlation of the 3' end, the type of mature transcript that leaves the nucleus, control the speed of mRNA transport from nucleus to cytoplasm, affects the number of transcripts arriving at the rough er and amount of gene product realized per unit of time

Translational control

Determines the degree to which mRNA is translated into a protein product

What features of mRNA affect whether translation occurs and how long the mRNA remains active

Presence of 5 prime cap and length of poly-A tail on 3 prime end

posttranslational control

Affects the activity of a protein product

Posttranslational control is accomplished by regulating what

Activation, degradation rate

Proteases

Enzymes that break down proteins and help regulate gene expression, regulate how long a protein remains active in the cell, confined to proteasomes or lysosomes to protect the cell

What is a gene mutation

A permanent change in the sequence of bases in dna

What are some effects of gene mutation

Complete inactivation of the protein, may not have any effects

_______________ mutations occur in sex cells

Germ-line

_________________ mutations occur in body cells

Somatic

Spontaneous mutations

Chemical changes in dna that lead to mirpairing during replication

What is the mutation rate

1 in 1,000,000,000 nucleotide pairs replicated

Induced mutations

Caused by mutagens such as radiation and organic chemicals or carcinogens

What are some environmental mutagens

Ultraviolet radiation, tobacco smoke

Point mutations

Involves a change in a single dna nucleotide, changes one codon to a different codon

What is one type of point mutation

Base substitution

What are some effects on proteins caused by point mutations

Makes it nonfunctional, reduces its functionality, or leaves it unaffected

Frameshift mutation

One or two nucleotides are either inserted or deleted from dna

Is a protein always rendered nonfunctional by a frameshift mutation

Yes

Development of cancer involves a series of accumulating ___________

Mutations

Proto-oncogenes

Stimulate cell division

What happens when proto-oncogenes are mutated

They become oncogenes that are always active

Tumor suppressor genes

Inhibit cell division

What happens when mutations occur in oncogenes and tumors supresor genes

The cell cycle is stimulated uncontrollably leading to tumor formation