Copyright © 2010 Pearson Education, Inc. CELLS: THE LIVING UNITS CHAPTER # 3(d)

Copyright © 2010 Pearson Education, Inc.

CELLS: THE LIVING UNITS

CHAPTER # 3(d)


Cell Cycle

• Defines changes from formation of the cell until it reproduces

• Includes:

• Interphase

• Cell division (mitotic phase)


Interphase

• Period from cell formation to cell division

• Nuclear material called chromatin

• Four subphases:

• G1 (gap 1)—vigorous growth and metabolism

• G0—gap phase in cells that permanently cease dividing

• S (synthetic)—DNA replication

• G2 (gap 2)—preparation for division

Copyright © 2010 Pearson Education, Inc. Figure 3.31

G1

Growth

SGrowth and DNA

synthesis G2

Growth and finalpreparations for

divisionM

G2 checkpoint

G1 checkpoint(restriction point)


Centrosomes(each has 2centrioles)

Nucleolus

Interphase

Plasmamembrane

Nuclearenvelope

Chromatin

Interphase


DNA Replication

• DNA helices begin unwinding from the nucleosomes

• Helicase untwists the double helix and exposes complementary chains

• The Y-shaped site of replication is the replication fork

• Each nucleotide strand serves as a template for building a new complementary strand


DNA Replication

• DNA polymerase only works in one direction

• Continuous leading strand is synthesized

• Discontinuous lagging strand is synthesized in segments

• DNA ligase splices together short segments of discontinuous strand


DNA Replication

• End result: two DNA molecules formed from the original

• This process is called semiconservative replication


AdenineThymineCytosineGuanine Old (template) strand

Two new strands (leading and lagging)synthesized in opposite directions

DNA polymerase

DNA polymerase

Laggingstrand

Leading strand

Free nucleotides

Old strand acts as atemplate for synthesisof new strandChromosome

Helicase unwindsthe double helix andexposes the bases

Old DNA

Replicationfork


DNA Replication

PLAYPLAY Animation: DNA Replication


Cell Division

• Mitotic (M) phase of the cell cycle

• Essential for body growth and tissue repair

• Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle


Cell Division

• Includes two distinct events:

1. Mitosis—four stages of nuclear division:

• Prophase

• Metaphase

• Anaphase

• Telophase

2. Cytokinesis—division of cytoplasm by cleavage furrow


G1

Growth

SGrowth and DNA

synthesis G2

Growth and finalpreparations for

divisionM

G2 checkpoint

G1 checkpoint(restriction point)


Cell Division

PLAYPLAY Animation: Mitosis


Prophase

• Chromosomes become visible, each with two chromatids joined at a centromere

• Centrosomes separate and migrate toward opposite poles

• Mitotic spindles and asters form


Prophase

• Nuclear envelope fragments

• Kinetochore microtubules attach to kinetochore of centromeres and draw them toward the equator of the cell

• Polar microtubules assist in forcing the poles apart


Early mitoticspindle

Early Prophase

Centromere

Aster

Chromosomeconsisting of twosister chromatids

Early Prophase


Spindle pole

Kinetochore Kinetochoremicrotubule

Polar microtubule

Late Prophase

Fragmentsof nuclearenvelope

Late Prophase


Metaphase

• Centromeres of chromosomes are aligned at the equator

• This plane midway between the poles is called the metaphase plate


Spindle

MetaphaseplateMetaphase

Metaphase


Anaphase

• Shortest phase

• Centromeres of chromosomes split simultaneously—each chromatid now becomes a chromosome

• Chromosomes (V shaped) are pulled toward poles by motor proteins of kinetochores

• Polar microtubules continue forcing the poles apart


Anaphase

Daughterchromosomes

Anaphase


Telophase

• Begins when chromosome movement stops

• The two sets of chromosomes uncoil to form chromatin

• New nuclear membrane forms around each chromatin mass

• Nucleoli reappear

• Spindle disappears


Cytokinesis

• Begins during late anaphase

• Ring of actin microfilaments contracts to form a cleavage furrow

• Two daughter cells are pinched apart, each containing a nucleus identical to the original


Contractilering atcleavagefurrow

Nuclearenvelopeforming

Nucleolusforming

Telophase

Telophase and Cytokinesis


Control of Cell Division

• “Go” signals:

• Critical volume of cell when area of membrane is inadequate for exchange

• Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks))


Control of Cell Division

• “Stop” signals:

• Contact inhibition

• Growth-inhibiting factors produced by repressor genes


Protein Synthesis

• DNA is the master blueprint for protein synthesis

• Gene: Segment of DNA with blueprint for one polypeptide

• Triplets of nucleotide bases form genetic library

• Each triplet specifies coding for an amino acid

PLAYPLAY Animation: DNA and RNA


Nuclearpores

mRNA

Pre-mRNARNA Processing

Transcription

Translation

DNA

Nuclearenvelope

Ribosome

Polypeptide


Roles of the Three Main Types of RNA

• Messenger RNA (mRNA)

• Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm



• Ribosomal RNA (rRNA)

• A structural component of ribosomes that, along with tRNA, helps translate message from mRNA



• Transfer RNAs (tRNAs)

• Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis

Copyright © 2010 Pearson Education, Inc. CELLS: THE LIVING UNITS CHAPTER # 3(d)

Documents

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dna replication slide

division slide

dna replication dna

dna replication dna

dna synthesis g

mitosis slide

new complementary strand