ch 19 - eukaryotic gene expression

Question 1

two features of eukaryotic genomes that are a major information processing challenge

Answer 1

1. the typical eukaryotic genome is much larger than that of a prokaryotic cell
2. cell specialization limits the expression of many genes to specific cells (not all genes are expressed in all cells)

Question 2

what is chromatin structure based on

Answer 2

successive levels of DNA packing

Question 3

eukaryotic DNA - contain what

Answer 3

precisely combined with a large amount of protein
contains an enormous amount of DNA relative to their condensed length

Question 4

histones

Answer 4

proteins
responsible for the first level of DNA packing in chromatin
DNA + histones = chromatin
Once DNA wraps around histone, it remains wrapped only leaving during replication

Question 5

chromosomes

Answer 5

60% protein by weight
most proteins are histones
hisontes help package and condense DNA

Question 6

nucleosome

Answer 6

in electron micrographs, unfolded chromatin has the appearance of beads on a string
each bead is a nucleosome
DNA wrapped almost twice around a core of 8 histone proteins

Question 7

second level of packing proteins

Answer 7

30 nm chromatin fiber
nucleosomes coming tighter together

Question 8

third level of packing proteins

Answer 8

the 30 nm fiber forms looped domains making up a 300 nm fier

Question 9

fourth level of packing proteins

Answer 9

the looped domains coil and fold, forming the metaphase chromosome

Question 10

why do the proteins fold and loop and etc

Answer 10

allows for lots of DNA to be packed into small amounts of space in our cell

Question 11

interphase chromatin is usually much less condensed than that of mitotich chromosomes
why?

Answer 11

replication occurs during synthesis so DNA needs to be open and accessible
transcription also occurs during interphase so DNA needs to be relaxed and open

Question 12

two types of chromatin - can be differentiated by stains

Answer 12

euchromatin
heterochromatin

Question 13

euchromatin

Answer 13

more open, stains more lightly- oppenness allows transcription enzymes access

Question 14

heterochromatin

Answer 14

more condensed
stains darkly
largely inaccessible to transcription enzyme
regulates whether a part of DNA can be transcribed or not

Question 15

cell differentiation

Answer 15

specialization in form and function of a cell to determine which genes are expressed at a time
only certain genes expressed in cerain cells, although all DNA exists in each cell

Question 16

how much of its genes do cells usually express

Answer 16

20% at a time
highly specialized cells only express a tony fracction of their genes
subset of genes expressed in the cells of each type is unique

Question 17

the differences between cell types are due to

Answer 17

differential gene expression
the expression of different geenes by cells with the same genome

Question 18

How do cells determine what genes are expressed and when

Answer 18

there is gene expression regulation at each stage
At DNA, RNA, and Protein stage there is control over what is used what is made and how long it stays around
there are control points that turn on, turn off, speed up, or slow down genes

Question 19

at the dna level, how is gene expression regulated

Answer 19

histone modification
DNA methylation

Question 20

histone modification

Answer 20

chemical modification of histone tails that affect the configuration of chromatin and thus gene expression
^tightly or loosely packed

Question 21

how are histones modified

Answer 21

histone acetylation
adding acetyl groups to histones
loosens chromatin structure and thereby enhances transcription
allows enzymes access to DNA for transcription

Question 22

DNA methylation

Answer 22

addition of methyl groups to certain bases in DNA
associated with reduced transcription
turns everything off so longterm inactivation of genes
removing methyl groups can turn on certain genes
once methylated genes stay that way from generation to generation
lacking methylation enzymes can cause abnormal embryonic development

Question 23

epigenetics

Answer 23

modifications that do not involve a change in DNA sequence, yet passed from generation to generation
not directly involving nuceotide sequence
DNA methylation and histone modifications

Question 24

RNA level how is gene expression regulated

Answer 24

things interact with transcription factors
control elements - proximal control elements or enhancers
segments of noncoding DNA that help regulate transcription by binding specific proteins
repressors

Question 25

enhancers

Answer 25

distal control elements that are far away from a gene
a given gene may have multiple enhancers, each active at a different time or in a different cell type or location
interactions between enhancers and transciption factors like activators or repressors control gene expression

Question 26

example of enhancers

Answer 26

activator binds to enhancer and stimulates transcription
helps assemble and position initiation complex on promoter and increases rate of gene expression
depending on available activators, only come genes are expressed via binding to enhancers

Question 27

repressors

Answer 27

some transcription factors function as repressors
inhibiting expression of a particular gene
some block binding of activators
some affect chromatin structure

Question 28

post-transcription ways to regulate genes

Answer 28

RNA processing
in altrenative RNA splicing, different mRNA molecules are produced from the same primary transcript
mRNA degradation

Question 29

mRNA degradation

Answer 29

mRNA can be degraded so no more proteins are made
RNA interference by single-stranded microRNAs
leads to degradation of an mRNA or block its traanslation
miRNA exhibits post-transcriptional control

Question 30

post-translation regulation

Answer 30

degrade or break fown protein
proteasomes - bind to protein and degrade them
regulate amount of time each protein functions in the cell