Chapter 18

Question 1

What are the evolutionary and energetic advantages of an operon?

Answer 1

The operon prevents the expression of genes when the products of that gene aren’t needed. It minimizes waste of resources. Found in bacterial cells

Question 2

Regulatory gene

Answer 2

gene from which the repressor is produced, located some distance from the operon it controls (regulates)

Question 3

Repressor protein

Answer 3

protein that prevents gene transcription by binding to the operator and blocking RNA polymerase

Question 4

Corepressor

Answer 4

molecule that cooperates with a repressor protein to switch a repressible operon off

Question 5

Promoter

Answer 5

part of the DNA strand to which transcription factors and RNA polymerase bind

Question 6

Operator

Answer 6

the part of the promoter that serves as the binding site for the repressor; the on/off switch of the operon

Question 7

Gene of operon

Answer 7

the gene(s) whose expression is controlled by the operator sequentially after the promoter

Question 8

Describe how an inducible operon is different from a repressible operon.

Answer 8

Inducible operons are usually off but can be turned on; repressible operons are usually on, but can be turned off

Question 9

What is differential gene expression?

Answer 9

the expression of different genes by cells with the same genome

Question 10

Why is differential gene expression important in multicellular eukaryotic organisms?

Answer 10

it leads to differences between cell types within the body

Question 11

How do chemical modifications to histones and DNA of chromatin influence chromatin structure and gene expression?

Answer 11

The structural organization of chromatin helps regulate gene expression in several ways; Highly packed heterochromatin cannot be expressed; Chemical modifications to chromatin influence expression

Question 12

Describe DNA methylation.

Answer 12

the addition of methyl groups (CH3) to certain bases in DNA, can condense chromatin and reduce transcription causing long-term inactivation of genes in cellular differentiation

Question 13

Describe histone acetylation.

Answer 13

acetyl groups are attached to an amino acid in a histone tail which promotes transcription by opening up the chromatin structure

Question 14

What are control elements?

Answer 14

segments of noncoding DNA that serve as binding sites for transcription factors

Question 15

How do control elements influence gene expression?

Answer 15

they give the cell better control of gene expression by requiring additional steps for transcription

Question 16

Compare and contrast distal and proximal control elements.

Answer 16

Proximal control elements are close to the promoter; A distal control element is far away from a gene

Question 17

Describe the process by which enhancers and activators encourage gene expression.

Answer 17

An activator protein binds to an enhancer to help initiation of gene transcription; Bound activators come into contact with mediator (helper) proteins through protein-mediated bending of the DNA; The mediator proteins help assemble and position the transcription complex

Question 18

Describe three mechanisms that occur after transcription that allow for fine-tuning of the gene expression.

Answer 18

A. Alternative RNA splicing can significantly expand the repertoire of a eukaryotic genome depending on which RNA segments are treated as exons and which as introns

B. With mRNA degradation, Each mRNA has a characteristic life span, determined in part by sequences in the 5′ and 3′ UTRs.

C. The length of time each protein functions is regulated by selective degradation; Cells mark proteins for degradation by attaching the protein ubiquitin to them

Question 19

What is morphogenesis?

Answer 19

The physical processes that give an organism its shape

Question 20

How does morphogenesis relate to differential gene expression?

Answer 20

It is controlled by differential gene expression; Gene expression orchestrates the developmental programs of animals and leads to the different cell types in a multicellular organism as well as the development of the shape of the organism

Question 21

What are cytoplasmic determinants?

Answer 21

substances in the egg that influence early development

Question 22

How do cytoplasmic determinants influence morphogenesis?

Answer 22

They are distributed unevenly in the unfertilized egg; As the zygote divides by mitosis, the daughter cells may contain different cytoplasmic determinants causing them to differentiate into separate cell types as well as giving shape and function

Question 23

Compare and contrast oncogenes and proto-oncogenes

Answer 23

Proto-oncogenes are genes that are responsible for normal cell growth and division;

Proto-oncogenes can be converted to oncogenes, cancer-causing genes, by viruses such a papilloma or hepatitis viruses

Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle and tumor formation

Question 24

How might proto-oncogenes be converted into oncogenes?

Answer 24

movement of DNA within the genome; amplification of a proto-oncogene; point mutations in the proto-oncogene or its control elements

Question 25

Describe how mutations lead to changes in gene regulation, which lead to cancer.

Answer 25

At the DNA level, a cancerous cell is usually has at least one active oncogene and several mutated of tumor-suppressor genes; these genes normally control cell life span and cell cycle; after mutation the cell may exhibited extended life span (allowing it to accumulate additional mutations) and/or an out of control cell cycle (causing it to divide rapidly and continuously leading to tumor formation); it takes mutation to several of theses genes to generate malignant cancer

Question 26

Ubiquitin

Answer 26

the protein used to mark other proteins for degradation

Question 27

Proteasomes

Answer 27

protein complexes which degrade unwanted or damaged proteins

Question 28

Trp operon

Answer 28

the operon that codes for enzymes used in the building of tryptophan; When tryptophan levels are high, it binds to the trp repressor protein, serving as a corepressor and turning the operon off

Question 29

Lac operon

Answer 29

an inducible operon that codes for enzymes used in the hydrolysis and metabolism of lactose into glucose and galactose

Question 30

Regulatory gene

Answer 30

gene responsible for controlling the expression of another gene

Question 31

Oncogenes

Answer 31

cancer-causing genes such as mutated tumor suppressing genes

Question 32

Proto-oncogenes

Answer 32

genes that are responsible for normal cell growth and division