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M1 > Nucleus > Flashcards

Nucleus Flashcards

1
Q

Nucleus

A
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2
Q

Nuclear Staining Varies Greatly Between Cell Types:

Some Nuclei Stain Pale and Have Uncondensed DNA -

Some Nuclei Stain Dark and Have Condensed DNA-

A

Euchromatin (dispersed and transcriptionally active DNA)

Heterochromatin (condensed and transcriptionally inactive DNA)

Cells with abundant heterochromatin are transcribing few genes

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3
Q

Why Do Nuclei Vary So Much?

A
  • Variations in nuclear function and framework
  • Variations in gene transcription
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4
Q
  • Complex of proteins + rRNAs that forms around the genes for ribosomal RNA
  • Site of assembly of ribosomal subunits
A

Nucleolus

Cells with prominent or multiple nucleoli produce larger amounts or ribosomes

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5
Q

DNA and Associated Proteins

A

Chromatin

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6
Q

DNA in Chromatin percentages

A
  • About 1% of DNA in chromatin actually codes for proteins (20,000 genes)
  • About 3% of DNA is “satellite” DNA (14-500 base sequences repeated 1000’s of times)
  • About 45% of DNA is formed from “moderately repeated” sequences of several thousand bases (transposons)
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7
Q

Allows Specific Labeling of All Chromosomes

A

In Situ Hybridization of Chromosome-Specific Repeated Sequences

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8
Q
  • Performed on squashed cells that are halted in metaphase by microtubule-destabilizing drugs
  • Used to assess chromosomal number, banding patterns, and possible chromosomal breakages
A

Karyotype Analysis

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9
Q

Occupy discrete territories within the nucleus

A

Interphase Chromosomes

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10
Q

In the Cell Cycle, 2 things can happen to chromosomal DNA:

A

Duplication and Separation

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11
Q

DNA Synthesis is Initiated When

A

a Kinase (Cyclin Dependent Kinase) Phosphorylates Rb

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12
Q

Cyclins and Cyclin-dependent Kinases

A
  • 11 Cd kinases are known, but only 4 seem important for the cell cycle
  • All 4 Cdk’s (Cdk1,2,4 & 6) can inhibit Rb and initiate DNA synthesis
  • Cdk2 phosphorylates Lamins and causes the disappearance of the nuclear envelope during mitosis
  • All Cdk’s must bind a protein, cyclin, to be active
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13
Q

Mitosis

A
  • Prophase (condensation)
  • Prometaphase (nuclear envelope breaks down)
  • Metaphase (chromosomes line up & attach to spindle)
  • Anaphase (chromosomes are pulled apart)
  • Telophase
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14
Q

Prophase

A
  • All chromosomes become greatly condensed
  • Chromosome 22 shrinks in length from 1.5 centimeters to about 2 micrometers (10,000 fold decrease in length)
  • Centrioles are duplicated and the mitotic spindle of microtubules is assembled
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15
Q

Metaphase

A
  • Nuclear envelope breaks down, permitting attachment of microtubules to the kinetochore (a complex of proteins attached to each chromosome at the centromere)
  • Chromosomes line up in the middle of the mitotic spindle
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16
Q

During Metaphase, ________ is released from sister chromatids except at the ________

A

cohesin; kinetochore

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17
Q

Anatomy of Kinetochore

A
18
Q

Anaphase

A
  • The so-called Anaphase Promoting Complex (APC), attached to the kinetochore, degrades cohesin
  • Chromatids move apart
  • APC also degrades cyclins, so that cyclin-dependent kinases stop functioning and mitosis completes itself
19
Q

As chromosomes move apart along kinetochore microtubules, so called _______ repel each other and push the two spindles apart

A

polar microtubules

20
Q

Mitosis vs. Meiosis

A

Unique features of 1st Meiotic Division:

  • Pairing of homologous chromosomes
  • Crossing over during 1st divison
  • 2nd Division
  • Haploid cells
21
Q

How do homologous chromosomes pair so precisely?

A

Chromosome tips attach to nuclear envelope during prophase 1 so that homologous pairs are aligned perfectly

22
Q

How do homologous chromosomes “recognize” each other?

A
  • Uncharacterized proteins prevent improper pairing?
  • Or Epigenetic Marks?
23
Q

What holds homologous chromosomes together?

A

Formation of Synaptonemal Complex (SCP1 protein)

24
Q

Proteins of Synaptonemal Complex

A
  • Synaptonemal Complex Protein 1 Binds adjacent DNA strands to each other
  • RAD51 recombinase protein causes cutting and splicing of DNA during Crossing Over
    • (Also found in lymphoid organs)
25
Q

Protein that is localized between paired chromosomes

A

SCP1

26
Q

What drives the switch from mitosis to meiosis?

A

Retinoic acid appears to be a key player in this process

27
Q

Gene Transcription Varies Between Cell Types

A
28
Q

Control of Gene Transcription

A
  • Each gene is marked by a specific sequence called the TATA box
  • The TATA box binds proteins needed for DNA transcription
  • All of these TATA binding proteins are only weakly active
  • To increase their activity, a Transcription Regulating Factor is required
  • 2000 different TRF’s are known; each cell produces only its own subset, leading to a unique pattern of DNA transcription for each cell
29
Q

Control Nanog gene to maintain pluripotency of stem cells

A

OCT4 & SOX2 Transcription Regulating Factors

30
Q

Transcription Factors Drive Cell Differentiation

A
31
Q

X-Chromosome Inactivation

A
  • In each female cell, one X-chromosome is randomly inactivated and condensed
  • In many cells, the X-chromosome becomes attached to the nucleolus

In some cells (white blood cells) the X-chromosome appears as a dark-staining Barr Body within the nucleus

32
Q

Lamin Proteins

A
33
Q

Lamin Proteins

A
  • Intranuclear varieties of intermediate filaments
  • Form the so-called nuclear lamina
  • Lamin A, B, and C subtypes are known
  • Interact with DNA, Transcription Regulating Factors (Rb protein), and the inner nuclear envelope to regulate nuclear shape and function
34
Q

Inherited abnormalities in Lamin A protein cause a syndrome, _______, with symptoms of ________

A

Progeria; accelerated aging

Symptoms include: weak bones, facial abnormalities, and distorted nuclear shapes;

Disease is very rare

35
Q

Abnormal Lamin A Protein Becomes Inapproperiately ________

A

Farnesylated

36
Q

Abnormally farneslated Lamin-A interacts abnormally with a major depressor of transcription called the ___________

A

retinoblastoma (Rb) Protein

Drugs that block the farnesylation of lamin-A relieve many of the symptoms of progeria in mice

37
Q

A Typical Cell Nucleus Possesses _________Nuclear Pores

A

3000-4000

38
Q

Pores are composed of

A

Nucleoporin proteins

39
Q

Nucleoporin Proteins

A
  • 456 individual protein molecules are found in each pore; there are about 30 varieties of nucleoporins
  • Function to bind and import proteins into the nucleus. Examples:
    • DNA, RNA polymerases
    • Transcription factors, histones
    • Nuclear proteins contain a sequence of basic amino acids termed a Nuclear Localization Sequence
40
Q

Nucleoporin Proteins Function:

A
  • Function to transport out of the nucleus proteins that bind to mRNA molecules
  • Function to export ribosomal subunits, which are assembled within the nucleus

M1 (48 decks)

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