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The Cytoskeleton

• A networked mesh of protein rods that support the cell, acting as scaffolding

• Also contain contractile units that allow for the movement of cells and for intracellular movement (organelle movement, vesicular transport)

• Three Types:

– Microtubules

– Microfilaments

– Intermediate filaments 1

Microfilaments

• Thin (but dense),

cross-linked strands

of actin (contractile

proteins)

• Involved in cell

motility and changes

in shape

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Intermediate Filaments

• Tough, stable,

permanent, rope-like

protein fibers

• Have high tensile

strength

• Helps cells resist

mechanical stress

and are found in

desmosomes for cell-

cell contact 3

Microtubules

• Long, hollow tubes

composed of tubulin.

Large in diameter

• Radiate from the

centrosome

• Determine cell shape

and organelle

distribution

• Important in

intracellular transport 4

Centrosome & Centrioles

• “microtubule organizing

center”

• Composed of two

centrioles (90o to each

other) and a granular

matrix

• Matrix generates

microtubules

• Centrioles generate

spindle fibers during cell

division 5

Cellular Extensions: Cilia

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2

Cellular Extensions: Flagella

• Sperm cells are the

only cells in the

human body with

flagella

• Similar to cilia but are

longer and allow cells

to propel themselves

• Use a whip-like

motion for locomotion

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Cellular Extensions: Microvilli

• Finger-like plasma membrane projections

• Increases plasma membrane surface area

• Typically found in absorptive cells

• Example: Lining of the small intestine 8

The Nucleus

• The “control center” of

the cell containing

genetic information

• The largest organelle of

the cell and is filled with

nucleoplasm

• Composed of: Nuclear

envelope, Nucleolus,

and Chromatin 9

The Nuclear Envelope

• Double membrane barrier

separated by a fluid-filled space

• Outer membrane is continuous

with RER & is studded with

ribosomes

• Inner membrane is lined with

nuclear lamina

• Two membranes come together

and form nuclear pores (entry and

exit point of particles) 10

Nucleoli

• Small, dense body

composed of RNA and

protein, where

ribosomes are

synthesized

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Chromatin

• Loosely coiled DNA fibers

and histone proteins,

condense to form

chromosomes.

• DNA + histone =

nucleosome

• Condense into

chromosomes during cell

division

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3

The Cell Cycle

• Cell cycles form a multi-

celled organism from one

original cell

• A series of changes cells go

through from the time they

are formed until they divide

• Promote growth and tissue

repair in organisms

• Involves phases and

checkpoints for quality

control

*Movie time! 13

Interphase • Cell growth and DNA

replication, “preparation

period”

• G1 Phase: Growth Phase

1, structures are

duplicated

• S Phase: Synthesis

Phase, DNA is replicated

• G2 Phase: Growth Phase

2, more structural

duplication, final

preparations

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DNA Replication

• Occurs before cell division

• DNA is uncoiled & H-bonds broken by a helicase

• DNA polymerase introduces complementary bases

• Replicated DNA is semi-conservative

• DNA condenses after replication 15

Mitosis

• Division of the nucleus:

– Prophase

– Metaphase

– Anaphase

– Telophase

• Cytokinesis: Division of the cytoplasm

• Exceptions: RBCs, nervous, skeletal &

cardiac tissue

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Mitosis

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Mitosis

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4

Protein Synthesis

• DNA provides the

information for

protein synthesis

• Two events:

– Transcription

– Translation

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Transcription

• Synthesis of

complementary

mRNA (messenger

RNA)

• Transcribes the

code for making

proteins and

transports it outside

the nucleus 20

Translation

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Translation

• Every mRNA codon

corresponds to an

amino acid

• Examples:

– CAC = Histidine

– CAA = Glutamine

– AAA = Lysine

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