Cell Biology Chapter 7 - The Nucleus and DNA Replication

Question 1

Key concepts – DNA Integrity is KEY!

Answer 1

The Nucleus Contains and Protects Most of the Eukaryotic Cell’s DNA

Question 2

Key concepts – DNA Integrity is KEY!

Answer 2

The nucleus is a highly specialized organelle committeed primarily to protecting, copying and transcribing DNA

The interior of the nucleus is highly compartmentalized

DNA copying, plus transcribing and splicing of RNA, are accomplished by large, highly specialized molecular complexes

Question 3

The Nuclear Envelope Is A Double Membrane Structure

Answer 3

the nuclear envelope
encloses the nucleoplasm
outer membrane of
the nuclear envelope is
continuous with the ER

Question 4

Evolution of the nucleus

Answer 4

The nucleus may have arisen by endosymbiosis, a process in which one prokaryotic cell engulfs another cell, which then becomes a primitive nucleus.

Question 5

The Outer Membrane of the Nuclear Envelope is Continuous with the Endoplasmic Reticulum

Answer 5

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Question 6

Nuclear Pore Complexes Regulate Molecular Traffic Into And Out Of The Nucleus

Answer 6

Key Features
layers of rings stacked on top of one another that span both nuclear membranes, linked to filamentous protein fibrils to form a basket structure
Pores are fomed at the places where the inner and outer membranes fuse together (not yet known how this happens)

Structure undergoes complex conformational changes when it transports material into and out of the nucleus

Question 7

The Interior Of The Nucleus Is Highly Organized And Contains Subcompartments

Answer 7

Nucleolus contains DNA that encodes ribosomal rRNAs
Nucleoli are sites of high transcriptional activity for rRNA genes
Sometimes there are more than one per cell
Nucleoli do not have a membrane – they are part of the nucleus

Question 8

The Nuclear Matrix Helps To Organize Chromosomes

Answer 8

Nuclear organization is not random
Chromosomes are compartmentalized into regions called chromosome territories
Nuclear matrix helps control the shape of chromosomes and regulate heterochromatin and euchromatin
Not known to contain any other cytoskeletal elements other than Nuclear Lamins.

Question 9

: Individual chromosomes occupy distinct areas of the nucleus called chromosome territories

Answer 9

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Question 10

The nuclear matrix is a network of filaments bound to the nuclear envelope and to DNA.

Answer 10

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Question 11

DNA Replication Occurs At Sites Called Replication Factories

Answer 11

DNA replication factories form large complexes in the nucleus devoted to copying DNA with 100% accuracy and no breaks
Replisome is the smallest functional unit in the factories and are responsible for copying one segment of DNA

Question 12

RNA Polymerase Complexes And Spliceosomes Are Distinct Structures Within The Nucleus

Answer 12

RNA polymerase complexes are responsible for transcribing the DNA sequence in genes into mRNA, rRNA, tRNA, and other RNAs
Spliceosomes are responsible for splicing the newly synthesized RNAs into their mature form

Question 13

DNA Polymerases

Answer 13

Are Enzymes That Replicate DNA

Question 14

DNA polymerases

Answer 14

DNA polymerases add deoxyribonucleotides to the 3’ end of DNA strand

DNA polymerases proofread their work
Have an exonuclease domain

Question 15

DNA Replication Is Semi-discontinuous

Answer 15

DNA replication begins at sites on chromosomes called origins of replication
E.coli have only one
Eukaryotes have several on each chromosome

What happens at the origin of replication in eukaryotes

Question 16

hexameric helicase

Answer 16

During Replication, Specialized Proteins Unwind And Separate The Two Strands To Form A Replication Fork

Question 17

DNA Replication Is Semi-discontinuous

Answer 17

If DNA builds DNA from a single-stranded template, how can it require a double strand to get started?

DNA replication requires an RNA primer (synthesized by primase)
leading/lagging strand
Okazaki fragments

DNA ligases join fragments of single-stranded DNA

Question 18

The helicase creating the replication fork is connected to

Answer 18

two DNA polymerase catalytic subunits, each of which is held onto DNA by a sliding clamp

Question 19

DNA Ligases

Answer 19

Join Fragments of Single-Stranded DNA

Question 20

Replication Of DNA At The End Of Chromosomes Requires Additional Steps

Answer 20

Role switching

Reverse Transcriptase Activity

Question 21

Cells Have Two Main DNA Repair Mechanisms

Answer 21

Excision repair systems
Mismatch repair
Recombination repair

Question 22

Recombination Systems Repair Large-Scale DNA Damage

Answer 22

Necessary as a last-ditch effort to repair DNA damage prior to cell division

Only rely on recombination to fix damage
Occurs either in the metaphase stage of mitosis or in meiosis
Arms of chromosomes occasionally break and swap pieces

Question 23

Mitosis Is Divided Into Stages

Answer 23

1879 - Walther Flemming described the motion of what he saw under microscope as “threads” (Greek, mitos) moving in an actively dividing cell

Question 24

Prophase

Answer 24

Prepares The Cell For Division

Gene Expression Halts

Question 25

Motors Contribute To The Formation Of The Mature Spindle In Prophase

Answer 25

Dynein motor proteins

Kinesin-related motor proteins (Eg5)

Question 26

Chromosomes Attach To The Mitotic Spindle During Prometaphase

Answer 26

Kinetochores attach chromosomes to the mitotic spindle

Question 27

Arrival Of The Chromosomes At The Spindle Equator Signals The Beginning Of Metaphase

Answer 27

Dynamic microtubules search for kinetochores throughout the cell by growing and shrinking in random directions from the centrosomes

Metaphase plate = spindle equator

Chromosome recombination takes place during metaphase

Question 28

Separation Of Chromatids At The Metaphase Plate Occurs During Anaphase

Answer 28

The onset of anaphase requires dissolving the connections between sister chromatids 
Anaphase Promoting Complex
Anaphase is subdivided into two phases:	
anaphase A 
anaphase B

Question 29

Figure 07.24:

Answer 29

Separation of replicated chromosomes during anaphase.

Question 30

Telophase - Cytokinesis

Answer 30

The structural rearrangements that occur in prophase begin to reverse during telephase
Cytokinesis completes mitosis by partitioning the cytoplasm to form two new daughter cells

Formation of a cortical actin-myosin filament network called the contractile ring

Fragmentation of non-nuclear organelles ensures their equal distribution in the daughter cells

For a brief moment, the plasma membrane between the two halves is ruptured, but it reseals almost instantaneously