Chapter 18.2 and 18.3 Flashcards Preview

Biology 1406 > Chapter 18.2 and 18.3 > Flashcards

Flashcards in Chapter 18.2 and 18.3 Deck (59):
1

Prokaryotes and eukaryotes alter gene expression in response to

their changing environment

2

In multicellular eukaryotes,

gene expression regulates the development and is responsible for differences in cell types
Ex. Muscle cell v. nerve cell

3

RNA molecules play many roles in

regulating gene expression in eukaryotes

4

Eukaryotic gene expression is regulated at

many stages

5

All organisms must regulate which genes are

expressed at any given time

6

In multicellular organisms regulation of gene expression is

essential for cell specialization

7

Almost all the cells in an organism are

genetically identical

8

Differences between cell types result from

differential gene expression, the expression of different genes by cells with the same genome

9

Abnormalities in gene expression can lead to

diseases including cancer

10

Gene expression is regulated at

many stages

11

Genes with highly packed heterochromatin are

usually not expressed

12

Chemical modifications to histones and DNA of chromatin

influence both chromatin structure and gene expression

13

In histone acetylation,

acetyl groups are attached to positively charged lysines in histone tails.

This loosens chromatin structure, thereby promoting the initiation of transcription

14

The addition of methyl groups (methylation) can condense chromatin; the addition of phosphate groups (phosphorylation)

next to a methylated amino acid can loosen chromatin

15

The histone code hypothesis proposes that

specific combinations of modifications, as well as the order in why they occur, help determine chromatin configuration and influence transcription

16

DNA methylation, the addition of methyl groups to certain bases in DNA, is

associated with reduced transcription in some species

17

DNA methylation can

cause long-term inactivation of genes in cellular differentiation

18

In genomic imprinting,

methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development

19

Although the chromatin modifications just discussed do not alter DNA sequence,

they may be passed to future generations of cells

20

The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence is called

epigenetic inheritance

21

Chromatin-modifying enzymes provide

initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery

22

Associated with most eukaryotic genes are multiple control elements,

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

23

Control elements and the transcription factors they bind are critical to

the precise regulation of gene expression in different cell types

24

To initiate transcription,

eukaryotic RNA polymerase requires the assistance of proteins called transcription factors

25

General transcription factors are

essential for the transcription of all protein-coding genes

26

In eukaryotes, high levels of transcription of particular genes depend on

control elements interacting with specific transcription factors

27

Proximal control elements are located close to

the promoter

28

Distal control elements, groupings of which are called enhances, may be

far away from a gene or even located in an intron

29

An activator is a

protein that binds to an enhancer and stimulates transcription of a gene

30

Activators have two domains,

one that binds DNA and a second that activates transcription

31

Bound activators facilitate a

sequence of protein-protein interactions that result in transcription of a given gene

32

Some transcription factors function as

repressors, inhibiting expression of a particular gene by a variety of methods

33

Some activators and repressors act indirectly by

influencing chromatin structure to promote or silence transcription

34

Transcription alone dow not account for

gene expression

35

Regulatory mechanisms can

operate at various stages after transcription

36

Such mechanisms allow a cell to

fine-tune gene expression rapidly in response to environmental changes

37

In alternative RNA splicing,

different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

38

The life span of mRNA molecules in the cytoplasm is a

key to determining protein synthesis

39

Eukaryotic mRNA is more long lived than

prokaryotic mRNA

40

Nucleotide sequences that influence the lifespan of mRNA eukaryotes reside in the

untranslated region (UTR) at the 3' end of the molecule

41

The initiation of translation of selected mRNAs can be

blocked by regulatory proteins that bind to sequences or structures of the mRNA

42

Alternatively, translation of all mRNAs in a cell may be

regulated simultaneously

43

For example, translation initiation factors are

simultaneously activated in an egg following fertilization

44

After translation,

various types of protein processing, including cleavage and the addition of chemical groups, are subject to control

45

Proteasomes are

giant protein complexes that bind protein molecules and degrade them

46

Noncoding RNAs play

multiple roles in controlling gene expression

47

Only a small fraction of DNA codes for proteins, and

a very small fraction of the non-protein-coding DNA consists of genes for RNA such as rRNA and tRNA

48

A significant amount of the genome may be

transcribed into noncoding RNAs (ncRNAs)

49

Noncoding RNAs regulate gene expression at two points:

mRNA translation and chromatin configuration

50

MicroRNAs (miRNAs) are

small single-stranded RNA molecules that can bind to mRNA.

These can degrade mRNA or block its translation

51

The phenomenon of inhibition of gene expression by RNA molecules is called

RNA interference (RNAi)

52

RNAi is caused by

small interfering RNAs (siRNAs)

53

siRNAs and miRNAs are similar but

form from different RNA precursors

54

In some yeasts siRNAs play a role in

heterochromatin formation and can block large regions of the chromosome

55

Small ncRNAs called piwi-associated RNAs (piRNAs) induce

heterochromatin, blocking the expression of parasitic DNA elements in the genome, known as transposons

56

RNA-based mechanisms may also block

transcription of single genes

57

Small ncRNAs can regulate

gene expression at multiple steps

58

An increase in the number of miRNAs in a species may have allowed

morphological complexity to increase over evolutionary time

59

siRNAs may have evolved first, followed by

miRNAs and later piRNAs