Chapter 7.6

Question 1

Why do cells regulate gene expression

Answer 1

1. Producing proteins cost large amounts of energy (p&e)
2. Each cell’s function is unique because it produces unique combinations of protein Each type of cell expresses a different subset of genes ( although each cell has a complete set of all genes it only expresses the ones needed to carryout its specific function). Not all genes in every cell is expressed some are turned off (( a hair cell would have the gene to make hemoglobin turned off and in a blood cell the genes to make hair) (Multicellular Eukaryotes)
3. It gives the cell flexibility to respond to changing conditions ( e.g genes expressing enzymes to digest a meal or antibodies during an infection- when the food or infection are the the gene is shut off) (p&e)
4. An intricate set of genetic instructions orchestrates the growth and the development of a multicellular organism
   (Multicellular Eukaryotes)

.

Question 2

In Eukaryotes, if each cell contains the same set set of genes how does it acquire it’s unique function?Why is each cell function unique

Answer 2

Each type of cell expresses a different subset of all the genes in each cell

Each cell’s function is unique because it produces unique combinations of protein

Question 3

OPERONS

Answer 3

In bacteria related genes are organized as OPERONS

They are groups of bacterial related genes that share one promoter

is a group of related genes plus a PROMOTER and an OPERATOR that control the transcription of the entire group at once.

Question 4

PROMOTER

Answer 4

Is the site to which RNA polymerase attaches to begin transcription

Question 5

OPERATOR

Answer 5

Is a DNA sequence located between the promoter and the protein encoding regions to which gene repressor proteins bind to stop the expression of a gene.

Question 6

REPRESSOR

Answer 6

a protein that binds to the OPERATOR in bacterial genes and prevents the transcription genes.

Is produced by a REGULATORY gene

Question 7

LAC OPERON

Answer 7

Consists of 3 gnes that encode lactose-degrading proteins plus the promoter and an operator that control their transcription

Question 8

The mechanisms for gene regulation in eukaryotic cells are

Answer 8

TRANSCRIPTION FACTORS

Question 9

TRANSCRIPTION FACTORS

Answer 9

Group of proteins that bind DNA at specific sequences that regulate transcription:

without Transription factors RNA polymerase cannot bind to a promoter or initiate transcription of a gene in the absence of transcription factors

They may bind to a gene’s PROMOTER or to an ENHANCER

Question 10

ENHANCER

Answer 10

a regulatory DNA sequence that lies outside the promoter ( they may also be located near it or within in)

Question 11

List the Regulatory mechanisms in eukaryotic cells

Answer 11

1. Transcription factors
2, DNA Availability /Methylation
3. Rna processing/ Different combinations of intron removal
4. m Rna Exit from nucleus
5. RNA Degradation
6. Protein Processing and degradation

Question 12

DNA AVAILABILITY/ Methylation

Answer 12

Chromosomes must be unwounded for genes to be expressed. A cell can tag an unneeded portion of DNA with a methyl group preventing gene expression and signaling the cell to fold more tightly. Transcription factors and RNA polymerase cannot access theDNA and so it is turned off

Question 13

RNA PROCESSING/ Intron removal

Answer 13

one gene can encode multiple proteins by removing or keeping different combinations of introns

Question 14

mRNA EXIT FROM NUCLEUS

Answer 14

A gene is silenced if it mRNA fails to leave the nucleus and attach to a ribosome

Question 15

RNA DEGRADATION/ micro Dna forms a double helix

Answer 15

1. some mRNA may not be stable and degrade before ring translated
2. microRNA produced by the cell may attach to the mRNA strand making it a double helix which cannot be translated and may degrade

Question 16

PROTEIN PROCESSING AND DEGRADATION

Answer 16

The gene is silenced when
1. if modifications to a newly synthesized polypeptide fail to occur ( folding e.g) that makes the the protein functional

2. If the protein fails to go to where it is needed
3. Like RNA, not all proteins are equally stable. Some degrade shortly after they are formed

Question 17

. What are some reasons that cells regulate gene expression?

Answer 17

Protein production costs a lot of energy; the regulation of gene expression avoids t he production of unnecessary proteins and therefore saves energy.

Question 18

. How do proteins determine whether a bacterial operon is expressed?

Answer 18

A repressor protein binds to an operator and prevents the genes in the operon from being transcribed.

Question 19

. How do enhancers and transcription factors interact to regulate gene expression

Answer 19

Transcription factors bind to certain DNA sequences to regulate transcription, for example by preparing a promoter site to bind RNA polymerase. Transcription won’t occur without these factors. Enhancers are sequences of DNA outside of the promoter. Transcription factors can bind to the enhancers to help regulate gene expression.

Question 20

What are some other ways that a cell controls which genes are expressed

Answer 20

Cells can keep DNA coiled or attach methyl groups to inactivate genes. During transcription different introns can be spliced out. mRNA can be contained in the nucleus or rapidly degraded. Proteins can also be degraded or modified in processing.

Question 21

How is GENE EXPRESSION controlled

Answer 21

By regulating TRANSCRIPTION

Question 22

Why is G E essential in prokaryotes

Answer 22

It allow the cel to take advantage of changing environment

2. Save energy

Question 23

Why is G E essential in multicellular Eukaryotes

Answer 23

1. allows genes to specialize
2. direct development
3. maintain homeostasis
4. save energy

Question 24

How is GENE EXPRESSION controlled in prokaryotes

Answer 24

by controlling the initiation in Transcription

( this is done by binding of proteins to regulatory sequences

Question 25

How is GENE EXPRESSION controlled in Eukaryotes

Answer 25

Transcription control operate at distance. Transcription Factors turn genes on and off by binding to promote and enhancer ( regulatory sequences)

Question 26

REGULATORY GENES

Answer 26

one that synthesizes REPRESSOR protein

Question 27

What are involved in regulating a gene expression in a bacteria

Answer 27

1. OPERON ( PROMOTER, OPERATOR, RELATED GENES)

2. REPRESSOR protein

Question 28

How is the REPRESSOR protein involved in gene regulation in prokaryotes

Answer 28

1. WHEN A PROTEIN IS NOT NEEDED
   The REPRESSOR protein attaches to the OPERATOR preventing the transcription of its gene.

WHEN A PARTICULAR PROTEIN NEEDS TO BE EXPRESSED ( e.g lactose is present so the protein lactase is needed to break it down)

Lactase binds to the REPRESSOR protein changing its shape which forces it to release from the the OPERATOR, so that initiation can began and the protein can be expressed ( lactase.

When lactose is no longer present the REPRESSOR protein rebinds to the OPERATOR

Question 29

There are 2 types of Operons

Answer 29

1. Negatively controlling Transcription ( removing a block)

2. Positive controlling Transcription ( turn on transcription)

Question 30

3 examples of a regulatory sequence

Answer 30

Are usually above the sequence to be expressed
1. Promotor ( in prokaryotes)

2. TATA BOX in ( eukaryotes)

3 Enhancers in eukaryotes

Question 31

Where does TRANSCRIPTION FACTORS bind on eukaryotes to allow ran polymerase to bind

Answer 31

1. promoter

2. Enhancer

Question 32

How does transcription factors prepare a promotor to receive RNA polymerase

Answer 32

1. the first transcription factor to bind is attracted to a part of the promoter called the TATA BOX.
2. 1st Transcription Factor attracts others including those that bind at the ENHANCER
   (In all TF binds to the TATA IN THE PROMOTOR and the ENHANCERS.
3. This triggers the RNA polymerase to bind and titian can begin

Question 33

Basically how does transcription factors turn genes off or on

Answer 33

by responding to stimuli