Chapter 13 Genetics

Front 1

Chromatin (Definition)

Back 1

made of DNA, histones, nonhistone proteins found in the cell nucleus

Front 2

Histones (Defination)

Back 2

small, highly-conserved proteins

Front 3

Histones (1)

Back 3

-positively charged tails
-lysine and arginine rich
-can be acetylated or methylated
-affect interaction with DNA

Front 4

Histones (2)

Back 4

-bind/neutralize (-) charged DNa
-half of all chromatine protein weight
-occur during S phase
-synthesize with DNA

Front 5

5 Types of Histones

Back 5

-H1, H2A, H2B, H3, and H4
-H2A, H2B, H3, and H4 form the nucleosome; aka core histones
-H1 is the linker DNA b/tw nucleosome

Front 6

Nonhistone proteins (NHPs)

Back 6

Functions
-Scaffold: backbone of chromosome; package DNA
-DNA replication
-Chromosome segregation
-Transcriptional regulation
-occur in different amts in different tissue

Front 7

Heterochromatin (Definition)

Back 7

- tightly condensed, transcriptionally inactive
- darkly stained region of chromosome
- highly compacted; even during interphase
- found in regions near centromere

Front 8

Euchromatin (Definition)

Back 8

-relaxed, transcriptionally active
-lightly stained regions of chromosome

Front 9

Faculative Heterochromatin (Definition)

Back 9

-dynamic, condensed or relaxed depending the conditions

Front 10

Total length of all DNA in human cells

Back 10

- 6 feet

Front 11

Diameter of nucleus of human cells

Back 11

- 6 microns

Front 12

Know the sizes of
- short region of DNA double helix
- nucleosomes: basic unit of chromatin
- chromatin fiber of packed nucleoosome

Back 12

- 20 Angstrom
- 100 Angstrom
- 300 Angstrom

Front 13

Nucleosome

Back 13

-160bp of DNA wrapped 2x around core of 8 histones (aka octamer; nucleosome core)
-2 each of H2A, H2B, H3, H4
- 7 fold compactions of DNA

Front 14

Linker DNA

Back 14

-B/tw nucleosomes
-40bp of DNA and histone H1

Front 15

100 Angstrom Fiber

Back 15

-"beads on a string"
- base sequences affect nucleosome positions along DNA
- Nucleosome spacing and structure affect genetic function

Front 16

2nd Level of Chromatin Compaction

Back 16

- 300 Angstrom fiber formed through supercoiling (superhelix)
- 6 fold compaction

Front 17

Higher level compaction of chromatin

Back 17

-40 fold compaction
- Radial loop-scaffold model
- Scaffold attachment regions (SARs)

Front 18

Radial loop-scaffold model

Back 18

-each loop contains 60-100kb of DNA tethered by NHP scaffold proteins
- SARs are sties where DNA is anchored to condensations scaffold; found at base of chromatin loops

Front 19

Higher level of compaction (2)

Back 19

- Other NHP gather loops into daisy-like-rosettes
- Condensins: compress the rosette centers into mitotic chromosomes

Front 20

All levels of compaction

Back 20

7 fold --> 40 fold -->250 fold

Front 21

Metaphase Chromosome

Back 21

- highly conserved banding patterns
- level where condensins mediate loops from the rosette centers into mitotic chromosomes
- giemsa-stained (G-banded)

Front 22

Eukaryotic Chromosome

Back 22

- many origins of replication
- replication occurs about 8 hours during S phase in actively dividing cells
-DNA pol assemble new DNA rate about 50 nucleotide per second

Front 23

Eukaryotic Chromosome (2)

Back 23

- each bidirectional replication is called a replication
- mammals: 10,000 origins of replication

Front 24

Telomeres

Back 24

- protective caps at ends of eukaryotic chromosomes
- preserve integrity of linear chromosomes
- contain DNA, protein, no genes

Front 25

Telomere Functions

Back 25

- prevent fusion with other chromosomes
- solve problem of replicating the 5' ends of chromosomes

Front 26

Watson's Dilemma

Back 26

-DNA synthesis occurs 5'-3' ONLY
-RNA primer is moved/degraded, there is a gap that is left
-How is complete synthesis of DNA achieved at 5' end of a linear chromosome

Front 27

DNA replication at the telomeres

Back 27

-telomeres are species-specific tandem (multiple) repeats with 3' overhang at end

Front 28

Telomerase

Back 28

-special pol made of RNA and protein
-binds specifically to telomere sequence
-Telomerase RNA is complementary to the tandem repeat 3'-AAUCCCAAU-5'

Front 29

DNA replication at the telomeres (2)

Back 29

-telomerase uses telomerase RNA as template to synthesize DNA in 5'-3' direction
-Telomerase repeats process several times by sliding further 3' after each round of synthesis

Front 30

Importance of Telomerase and Telomere maintenance to cell proliferation

Back 30

-Telomeres are essential for cell viability
-Yeast mutants that lack telomerase lose 3 bp of DNA per generation from chromosome ends

Front 31

Importance of Telomerase and Telomere maintenance from chromosome ends (2)

Back 31

Human Cells
-Actively dividing cells express telomerase (i.e. germ cells, stem cells)
-Terminally-differentiated cells don't express telomerase

Front 32

Importance of Telomerase and Telomere maintenance from chromosome ends (3)

Back 32

Human Cells (cont'd)
-Somatic cells can be immortalized in culture by expressing telomerase
-Tumor cells have high telomerase activity

Front 33

Centromeres are essential for chromosome segregation

Back 33

-centromeres appear as constrictions on chromosomes
- attachment to spindle fibers; tightly compacted
- contained w/in blocks of repetitive, noncoding sequences (satellite DNA)

Front 34

Satellite DNA

Back 34

- consists of short sequence (5-300 bases in length)

Front 35

Function of Centromeres

Back 35

- Hold sister chromatids together
- Kinetochore

Front 36

Dynamic interactions of cohesin during mitosis and meiosis

Back 36

- Just after S phase cohesin assoc along each entire chromo
- Entry into mitosis/meiosis, cohesin is lost along chromo arms but maintained at centromere

Front 37

Dynamic interactions of cohesin during mitosis and meiosis (2)

Back 37

- At start of anaphase in mitosis or anaphase II in meiosis, cohesin are cleaved --> separation of sister chromatids

Front 38

Anaphase vs Anaphase II

Back 38

-anaphase: cohesin is cleaved; sister chromatids separate; however remains at centromere to hold sister chromatids
-anaphase II: cohesin is cleaved; segregation of sister chromatids

Front 39

Kinetechore

Back 39

- specialized structure that forms at centromere and is attachment site for microtubules
- structure composed of DNA and protein that help power chromosome mov't; attachment to microtubules

Front 40

Yeast Centromere

Back 40

- Sequence: autonomously replicating sequences (ARSs) consist of an A-T rich region
- ARSs permit replication of plasmids in yeast cells
- Cut using recombinant; attach plasmid

Front 41

Eukaryotic Chromatin (Types)

Back 41

- Heterochromatin
- Facultative Heterochromatin
- Euchromatin

Front 42

Position-Effect Variegation

Back 42

- "good genes in bad neighborhood"
- chromosomal rearrangement (inversion or translocation) places gene next to highly compacted heterochromatin near the centromere, gene's expression ceases

Front 43

Position-Effect Variegation (2)

Back 43

- when normally euchromatic genes come into vicinity of heterochromatin, the heterochromatin can spread into euchromatic regions, shutting off gene expression in cells where the heterochromatin invasion takes place
- Facultative heterochromatin

Front 44

Epigenetic silencing

Back 44

- reversible inactivation of transcription because of change in chromatin structure

Front 45

Epigenetic inheritance

Back 45

- inheritance of chromatin status from one generation to the next
-affects gene expression but not DNA sequence

Front 46

Epigenetic marks

Back 46

- can be histone modifications or DNA mehtylation (5-methyl-cytosine)

Front 47

X-chromosome Inactivation

Back 47

-observable during interphase as darkly stained heterochromatin
- aka Barr bodies
- example of facultative heterochromatin

Front 48

X-chromosome Inactivation (2)

Back 48

-in mammals occurs through epigenetic silencing of the entire X chromosome

Front 49

Dosage Compensation

Back 49

- makes up for dosage imbalance of X-linked genes
- also occurs in other organisms but through a different mechanism

Front 50

Monoallelic expression

Back 50

-autosomes have biaallelic expression

Front 51

XX cells

Back 51

- one X-chromosome chosen at random to be silenced
-darkly staining barr body
-most X-linked genes expressed at equivalent levels in XX and XY cells

Front 52

X-inactivation status

Back 52

-propagated/maintained in all progeny cells

Front 53

X-inactivation

Back 53

-occurs early in embryogenesis in every cell
-random inactivation of one X-chromo in every cell
-every cell will have on active and one inactive (XXa) (XXj)
-almost all x-linked genes on inactive X are not transcribed

Front 54

Progeny somatic cells (X-inactivation)

Back 54

-will have same X inactivated
-reactivation of Xj occurs in germ cells

Front 55

Xist

Back 55

-noncoding RNA expressed only from the inactive X
-binds to a specific region on the active X
-X-inactivation center (XIC) and initiates inactivation of the entire chromosome