CHAPTER 13.1-13.3 (HALF OF FINAL)

Question 1

regular gene

Answer 1

normally located outside the operon, this codes for a dna-binding protein that acts as a repressor. the repressor controls whether the operon is active or not

Question 2

promoter

Answer 2

a short sequence of DNA where RNA polymerase first attaches to begin transcription of the grouped genes. basically, a promoter signals the start of the operon and the location where transcription begins

Question 3

operator

Answer 3

a short portion of DNA located before the structural genes. If a repressor is attached to the operator, then transcription cannot occur; conversely, if a repressor is not attached, then transcription can occur. in this way, the operator controls transcription of structural genes

Question 4

Structural genes

Answer 4

these genes code for the enzymes and proteins involved in the metabolic pathway of the operon. the structural genes are transcribed as a unit

Question 5

trp operon

Answer 5

tryptophan, an essential amino acid synthesized by the enzymes coded for in the trp operon.

Question 6

corepressor

Answer 6

tryptophan is called the corepressor. repressible operons are usually involved in anabolic pathways that synthesize a substance needed by the cell.

Question 7

repressible operon

Answer 7

the enzymes are said to be repressible, and the entire unit is called a repressible operon.

Question 8

inducer

Answer 8

because the presence of lactose brings about expression of genes, it is called an inducer of the lac operon.

Question 9

E. coli

Answer 9

if both glucose and lactose are present, then E. coli preferrentially breaks down glucose.

Question 10

cyclic AMP

Answer 10

the molecule that accumulates when glucose is absent. it is derived from ATP, but only has one phosphate group, which is attached to ribose at two locations. binds to a molecule called the catabolite activator protein (CAP) and the complex attaches to DNA. this exposes the promoter to rna polymerase which is now better able to bind so the genes are transcribed.

Question 11

types of control in eukaryotic cells that can modify the amount of gene product

Answer 11

chromatin structure, transcriptional control, posttranscriptional control, translational control, and posttranslational control

Question 12

transcriptional control

Answer 12

the degree to which a gene is transcribed into mRNA determines the amount of gene product. in the nucleus, transcription factors may promote or repress transcription, the first step in gene expression

Question 13

posttranscriptional control

Answer 13

involves mRNA processing and how fast mRNA leaves the nucleus

Question 14

translational control

Answer 14

occurs in the cytoplasm and affects when translation begins and how long it continues. small interfering RNA molecules (siRNA) are known to regulate translation. in addition, any condition that can cause the persistence of the 5’ cap and 3’ poly-A tail can affect the length of translation. Excised introns may also have effects on the life span of mRNA.

Question 15

posttranslational control

Answer 15

also takes place in the cytoplasm and occurs after protein synthesis. only a functional protein is an active gene product

Question 16

chromatin

Answer 16

the dna in eukaryotes is always associated with a variety of proteins, and together they make up a stringy material called chromatin.

Question 17

histones

Answer 17

proteins that play an important role in the compaction of the DNA, as well as in eukaryotic gene regulation. regulate accessebility to dna

Question 18

euchromatin

Answer 18

more loosely packed

Question 19

heterochromatin

Answer 19

more densely packed. not transcribable

Question 20

barr body

Answer 20

a dramatic example of heterochromatin in mammalian females.

Question 21

epigenetic inheritance

Answer 21

variations in the pattern of inheritance are not due to changes in the sequence of the DNA nucleotides.

Question 22

genomic imprinting

Answer 22

during this, either the mother’s or the father’s gene, but not both, is methylated during gamete formation. if a gene is methylated, the gene is not expressed, even if it is a normal gene in every other respect.

Question 23

transcription factors

Answer 23

every cell contains many different types of these, and they are proteins that help regulate transcription by assisting the binding of the RNA polymerase to the promoter. the absence of even just one can prevent transcription from occurring.

Question 24

transcription activator

Answer 24

transcription may not begin without the assistance of a DNA-binding protein called a transcription activator

Question 25

enhancers

Answer 25

transcription activators bind to regions of the DNA called enhancers, which may be located some distance from the promoter. A hairpin loop in the DNA brings the transcription activators attached to the enhancer into contact with the transcription factor complex.

Question 26

RNA interferene

Answer 26

because both miRNA and siRNA molecules interfere with the normal gene expression pathways, the process is often referred to as RNA interference

Question 27

proteases

Answer 27

just how long a protein remains active in a cell is usually regulated by the use of proteases, enzymes that break down proteins

Question 28

proteasomes

Answer 28

to protect the cell, proteases are typically confined to the lysosomes or special structures called proteasomes

Question 29

gene mutation

Answer 29

a permanent change in the sequence of bases in DNA

Question 30

spontaneous mutations

Answer 30

may arise as a result of abnormalities in normal biological processes

Question 31

induced mutations

Answer 31

may result from exposure to toxic chemicals or radiation, which induce changes in the base sequence of dna

Question 32

mutagens

Answer 32

induced mutations are caused by mutagens, environmental factors that can alter the base composition of DNA. many mutations are also carcinogens (cancer-causing mutations)

Question 33

DNA repair enzymes

Answer 33

wherever there are two thymine molecules next to one another, uv radiation may cause them to bond together, forming thymine dimers. a kink results in the dna. usually, these dimers are removed by dna repair enzymes, which constantly monitor dna and fix any irregularities

Question 34

point mutations

Answer 34

involve a change in a single dna nucleotide, which alters transcription and possibly changes the specific amino acid.

Question 35

frameshift mutations

Answer 35

occur most often when 1 or more nucleotides are either added or deleted from DNA. results in a completely new sequence of codons, yielding a nonfunctional protein