Lecture 7

Question 1

The different cell types of a multicellular organism contain the same DNA

Answer 1

Different cell types produce different sets of proteins

A cell can change the expression of its genes in response to external signals

Question 2

Gene expression can be regulated at various steps from

Answer 2

DNA to RNA to protein

Question 3

Differentiated cells contain all of the genetic instructions needed to direct the formation of a complete organism

Answer 3

This showed that nucleus of skin cells contain all of the genes necessary to grow a fully functioning organism

Question 4

Gene expression in eukaryotic cells can be controlled at various steps

Answer 4

Most genes are under transcriptional regulation: Prevent transcription = saves energy; Energy saving and response time are inversely related

can repress or activate transcription (in eukaryotes, RNA processing is used (whether or not it’s spliced))

Most genes (both eukaryotes and prokaryotes) are regulated at step 1 (transcriptional control): Translation is one of the most energetically expensive processes, inactivating TRSANSCRIPTION will avoid this

1) transcriptional control
2) RNA processing contol
3) mRNA transport and localization control
4) mRNA degradation control
5) Translation control
6) Protein degradation control
7) Protein activity control

Question 5

Transcription regulators bind to reguatory DNA sequences

Answer 5

A transcription regulator interacts with the DNA double helix

Both eukaryotic and prokaryotic have transcription regulators turn transcription on or off

These proteins INTERACT with DNA, but have NO enzymatic activity (can’t break it open)

Question 6

Many Transcription regulators bind to DNA as dimers

Answer 6

Transcription regulators bin as dimers = ability to form combinations = able to regulate all 20,000+ gene

Usually heterodimers

Question 7

Transcription switches allow cells to respond to changes in their environment

Answer 7

Repressors turn genes off and activators turn them on

Question 8

A cluser of bacterial genes can be transcribed from a single promoter

Answer 8

Many bacteria organize their genes into strcutres known as OPERONS (only in bacteria, not eukaryotes)

ALL are regulated with the same control sequences

Either the ENTIRE operon is made or none of it is

Operons contain several different genes that are part of a biosynthesis pathway; has just ONE operator

Question 9

Genes can be switched off by repressor proteins

Answer 9

Repressor proteins repress transcription

Cell where tryptophan is high do not need to make any; prtoein synthesis slows down, tryptophan binds to Trp repressor, repressor changes shape to bind to the operator = transcription off

Cell where tryptophan is low will need to make some: Cell has inactive repressor = RNA polymerase can attach

Question 10

Repressors ONLY bind to the

Answer 10

Operator

Question 11

Genes can be switched on by

Answer 11

Activator proteins

Activate processes, increase the efficiency of transcription

Question 12

The lac Operon is controlled by an activator and a repressor

Answer 12

In E coli, lac operons primarily use glucose; in normal situation, lac operon is off; lac operon enablles cells to use lactose (E coli will usually want gloucose, uses lac operon to consume lactose ONLY when glucose is absent); lactose is a dissacharide = harder to use

Activator can ONLY bind to an activator binding site

Repressor can ONLY bind to operator

When glucose is abundant, lac repressor acts as an active repressor

Question 13

Eukaryotic transcription regulators control gene expression from a distance

Answer 13

Eukaryotic transcription regulators help initiate transcription by recruiting chromatin-modifying proteins

Question 14

In eukaryotes, gene activation can occur at a distance

Answer 14

Big distance from genes and regulatory sequences

2 types of transcription factors in eukaryotes:

1) General transcription factors (be with promoter and most will be the same)
2) Regulatory transcription factor (differ b/w cells; Do NOT interact with promoter; EITHER with enhancer or operator)

Question 15

Transcription of OFF by default

Answer 15

One of the functions of activators is to restructure the DNA (i.e. modify histone tails: add negative functional groups, histones will become less positive)

Chromatin remodeling complexes move histone down

Question 16

Eukaryotic transcriptional activators can rectruit chromatin-modifying proteins to help initiate

Answer 16

Gene transcription

Ways that transcription initiation can start; all triggered by transcriptional activator

Question 17

The arrangement of chromosomes into looped domains keeps enhancers

Answer 17

In chek

Question 18

Animal and plant chromosomes are arranded in

Answer 18

DNA loops

Both plants and animals: Enhancers pulled close to genes when they’re in the loop even though they are many bases away

Question 19

Generating Specialized Cell Types: Eukaryotic genes are controlled by combinations of transcription regulators

• The expression of different genes can be coordinated by a single protiein
• Combinatorial control can also generate different cell types

Answer 19

Trancription regulators work together as a “committee” to control the expression of a eukaryotic gene

One of the biggest complexes in your cell; many proteins function

A single transcription regulator can coordinate the expression of many different genes
-One molecules can regulate several different genes

Combinations of a few transcription regulators can generate many cell types during development
-Precursor cell receives special signal to make protein; once it happens early on, ALL progeny cells will maintain that protein

Question 20

Trancription regulators can be used to experimentally direct the formation of specific cell types in culture

Answer 20

A small number of transcription regulators can convert one differentiated cell type directly into another
-This happens in LAb, not nature

A combination of transcription regulators can induce a differentiated cell to de-differentiate into a puripotent iPS cell

• Genes introduced into fibroblast nucleus -> cells allowed to divide in culture -> iPS cell -> differentiate in culture
• Induce transcription factors in fibroblast to de-differentiate it (no longer a specialzed cell)
• De-differentiate fibroblast into a cell that has the ability to turn into anything
• IN nature, once a fcell has been differentiated, it stays as that cell type
• Fibroblast = type of cell common in extracellular matrix

Question 21

Differentiated cells maintain their identity

Answer 21

A positive feedback loop can generate CELL MEMORY: generated by + feedback loop
-Parent cell: Gene A is not on (deactivated) -> signal from neighboring cell turns ON expression of gene -> transcription of self is activated and maintiant in ALL progeny cells (regardless of the presence of the signal) (cell “remembers” to transcribe the product without the presence of the signal)

Formation of 5-methylcytosine occurs by methylation of a cytosine base in the DNA helix

• Modification of DNA via methylation
• Add methyl to DNA, same segment in progeny cells will also be methylated (inherited)
• Methylate DNA = Add methyl group
• Continued in ALL progeny
• Method of REPRESSING TRANSCRIPTION
• Always methylating a C next to a G (NOT all CG pairs are methylated, these are the only ones that have the option to be)
• Newly synthesized strands will NOT be methylated
• Keeps transcripts off
• DNA methylation patterns can be faithfully inherited when a cell divides
• ALWAYS methylated on a cytosine next to a guanine; NOT all cytosines next to guanines will be methylated
• If you have it on one strand, the partner strand will also be methylated at this site
• Parent strand is methylated, newly synthesized strand is NOT

Hisonte modifications may be inherited by daughter chromosomes

• Histone modifications are also inherited
• Daughter cells receive about HALF of the nucleosomes; 1/2 will go through and modify the ones that aren’t modified; eventually all will be modified in the same way that the parent cell was
• CAN be inherited; when DNA replicated, daughter cells receive about half of those nucleosomes; modified ones attract modification proteins, unmodified ones will not

Question 22

3 Ways special cell types can be generated

Answer 22

Cell memory

DNA methylation

Histone modification