Bio - Exam 4 - Gene Regulation and Developmental Biology

Controlling gene expression is often accomplished by

controlling transcription initiation

Regulatory proteins bind to

DNA

this may block or stimulate transcription

Prokaryotic organisms regulate gene expression in response to

their environment

eukaryotic cells regulate gene expression to

maintain homeostasis in the organism

Gene expression is often controlled by

regulatory proteins binding to specific DNA sequences

Regulatory proteins gain access to the

bases of DNA at the major groove

Regulatory proteins possess

DNA-binding motifs

Prokaryotic Gene Regulation: control of transcription initiation - POSITIVE control

increases frequency of initiation of transcription

(activators enhance binding of RNA polymerase to promoter, effector molecules can enhance or decrease)

Prokaryotic Gene Regulation: control of transcription initiation - NEGATIVE control

decreases frequency

(repressors bind to operators in DNA, allosterically regulated, respond to effector molecules - enhance or abolish binding to DNA)

allosteric regulation

a process in biology where an enzyme's activity is controlled by a regulatory molecule binding to a site other than the active site, called an allosteric site

Prokaryotic cells often respond to their environment by

changes in gene expression

Genes involved in the same metabolic pathway are organized in

operons

Induction

enzymes for a certain pathway are produced in response to a substrate

Repression

capable of making an enzyme but does not

lac operon

contains genes for the use of lactose as an energy source

genes involved with the lac operon

b-galactosidase (lacZ), permease (lacY), and transacetylase (lacA)

(the gene for the lac repressor is linked to the rest of the lac operon)

The lac operon is _______________ by a repressor protein

negatively regulated

lac repressor binds to the operator to

block transcriptionlac

In the presence of lactose, an inducer molecule like allolactose

binds to the repressor protein

this makes it so the repressor can no longer bind to the operator

then transcription proceeds

allolactose

an inducer molecule

trp operon

genes for the biosynthesis of tryptophan

for trp operon, the operon is not expressed when

the cell contains sufficient amounts of tryptophan

for trp operon, the operon is expressed when

levels of tryptophan are low

trp repressor is a

helix-turn-helix protein that binds to the operator site located adjacent to the trp promoter

the trp operon is _________ by the trp repressor protein

negatively regulated

trp repressor binds to the operator to

block transcription

binding of the trp repressor to the operator requires

a corepressor which is tryptophan

low levels of tryptophan prevent the repressor from

binding to the operator

repressors undergo a ________ when the tryptophan binds, allowing the repressor to bind to the operator in the major grooves

shape change

eukaryotic regulation control of transcription is

more complex

Major differences between eukaryotic and prokaryotic regulation

eukaryotes have DNA organized into chromatin (complicates protein-DNA interaction)

eukaryotic transcription occurs in the nucleus

For eukaryotic regulation, the amount of DNA involved in regulating eukaryotic genes is

much larger

Chromosomes are compacted by

proteins called histones (wraps around)

Eukaryotic regulation is more complicated because

RNA polymerase and transcription factors need to bind to DNA, not to histones

Development biology is turning

one cell into a functional organism

sperm and egg are haploid →

1 cell (zygote) diploid

the zygote undergoes

cleavage

cleavage leads to

a hollow tiny ball of cells that does mitosis but doesn’t grow (skipped G1 phase)

the hollow ball of cells undergoes

gastrulation

gastrulation includes

cell movement by actin and formation of germ layers

gastrulation leads to the

gastrula

germ layers

ectoderm, mesoderm, endoderm

ectoderm

outside, skin, nervous system

mesoderm

middle, inside except gut, connective tissue, bone, blood, kidney, muscle

endoderm

inside, digestive tract, liver, pancreas, lungs

Steps of development

Fertilization, Cleavage, Gastrolation, Organogenesis

Step 1: Fertilization

fusion, haploid gametes into diploid cell

Step 2: Cleavage

mitosis, but with no growth between cell divisions (no G1)

Step 3: Gastrolation

Forms gut tube and germ layers

Step 4: Organogenesis

Formation of organs

Divisions of cellular labor

the specialization of organelles within a cell for specific functions

Morphogens

signaling molecules that determine the fate of cells during embryonic development

concentration of these determines type (thresholds)

how genes are turned on or off

High concentrations of morphogens

ectoderm

medium concentration of morphogens

mesoderm

low concentration of morphogens

endoderm