7.dna replication

8/10/2019 7.DNA Replication

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Fundamentals of Cell Biology

Chapter 7: The Nucleus and DNA

Replication


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Chapter foci:

Examine the anatomy of the nucleus

Introduction to the protein complexes necessary for

building, replicating, and maintaining the structureof DNA

Discussion of mitosis and the importance of the

cytoskeleton in regulating mitosis

Chapter Summary: The Big Picture (1)


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Chapter Summary: The Big Picture (2)

Section topics:

The nucleus contains and protects most of a

eukaryotic cells DNA

DNA replication is a complex, tightly-regulatedprocess

Mitosis separates replicated chromosomes


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The nucleus contains and protects most of

a eukaryotic cells DNA

Key Concepts:

The nucleus is a highly-specialized organelle

committed 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.


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The nuclear envelope is a double

membrane structure

the nuclear envelope encloses the

nucleoplasm

outer membrane of the nuclear

envelope is continuous with the ER


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Nuclear pore complexes regulate

molecular traffic into and out of the nucleus

layers of rings stacked

on top of one another

that span the nuclear

membranes, linked tofilamentous protein

fibrils to form a basket

structure

structure undergoescomplex conformational

changes when it

transports material into

and out of the nucleus


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The interior of the nucleus is highly

organized and contains subcompartments

nucleolus contains DNA that

encodes ribosomal RNAs

nucleoli are sites of high

transcriptional activity forrRNA genes


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The nuclear matrix helps to organize

chromosomes

chromosomes are

compartmentalized into

regions called chromosome

territories nuclear matrix helps control

the shape of chromosomes

and regulate

heterochromatin andeuchromatin


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DNA replication occurs at sites called

replication factories

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 thefactories and are responsible for copying one

segment of DNA


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RNA polymerase complexes and

spliceosomes are distinct structures within

the nucleus 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


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DNA replication is a complex, tightly-

regulated process Key Concepts (1):

DNA replication in all organisms is performed by a

small number of highly-conserved proteins.

Both prokaryotes and eukaryotes express differentforms of DNA polymerase, the enzyme responsible

for synthesizing DNA.

DNA replication begins at specific sites called origins

of replication. During replication, double-stranded DNA is unwound

and dissociated into single strands that serve as

templates for synthesis of complementary DNA

strands.


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Key Concepts (2):

DNA synthesis occurs only in the 5-to-3direction.

DNA polymerases must bind a double-stranded portion of

a DNA molecule to begin synthesis. Most often, the double

strand consists of the template DNA strand and a short,

complementary RNA primer.

DNA ligase connects individual pieces of newly

synthesized DNA to form a complete strand.

The enzyme telomerase adds extra DNA to the ends of

chromosomes to protect them from degradation.

DNA replication is a complex, tightly-

regulated process


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DNA polymerases are enzymes that

replicate DNA


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DNA polymerases

DNA polymerases add

deoxyribonucleotides to

the 3end of DNA strand

DNA polymerasesproofread their work


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DNA replication is semi-discontinuous

DNA replication begins

at sites on

chromosomes called

origins of replication During replication,

specialized proteins

unwind and separate

the two strands to forma replication fork


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The replication complex


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DNA replication is semi-discontinuous

DNA replication requiresan RNA primer

leading/lagging strand

Okazaki fragments DNA ligases join

fragments of single-

stranded DNA


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Replication of DNA at the end of

chromosomes requires additional steps


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Cells have two main DNA repair

mechanisms

Excision repair systems

Mismatch repair

Recombination repair


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Key Concepts: The function of mitosis is to safely separate

replicated chromosomes into two daughter cells.

Mitosis is divided into five phases, based largely onmorphological changes in the location and

arrangement of chromosomes.

The microtubule cytoskeleton, including microtubule

motor proteins, is essential for proper segregation ofchromosomes.

The actin cytoskeletonis required for the actual

division of one cell into two daughter cells following

mitosis.

Mitosis Separates Replicated

Chromosomes


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Mitosis is divided into stages

1879 - Walther Flemming

described the motion of what

he saw under microscope

asthreads

(Greek, mitos)

moving in an actively

dividing cell


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Prophase prepares the cell for division


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Motors contribute to the formation of

the mature spindle in prophase

Dynein motor proteins

Kinesin-related motor proteins


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Chromosomes attach to the mitotic

spindle during prometaphase

Kinetochores attach chromosomes to the mitoticspindle

A i l f th h t th


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Arrival of the chromosomes at the

spindle equator signals the beginning

of metaphase Metaphase plate = spindle equator


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Separation of chromatids at the metaphase

plate occurs during anaphase

The onset of anaphase requires dissolving the

connections between sister chromatids

APC


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Separation of chromatids at the metaphase

plate occurs during anaphase

Anaphase is subdivided into two phases:

anaphase A

anaphase B


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Telophase - Cytokinesis

The structural rearrangements that occur inprophase begin to reverse during telophase

Cytokinesis completes mitosis by partitioning the

cytoplasm to form two new daughter cells

Fragmentation of non-nuclear organelles

ensures their equal distribution in the daughter

cells

7.dna replication

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