Chapter 3: The Cellular Level of Organization

1
Chapter 3 The Cellular Level of Organization
2
The Cell

• Performs all life functions

Figure 31
3
Sex Cells

• Sex cells (germ cells)
• reproductive cells
• male sperm
• female oocytes (eggs)

4
Somatic Cells

• Somatic cells (soma body)
• all body cells except sex cells

5
Organelle Functions
Table 31 (1 of 2)
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Organelle Functions
Table 31 (2 of 2)
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Functions of Cell Membrane (1 of 2)

• Physical isolation
• Monitors Regulates exchange with environment
• extracellular fluid composition
• chemical signals
• ions and nutrients enter
• waste and cellular products released
• Structural support
• anchors cells and tissues

8
Structures and functions of the cell membrane
9
The Cell Membrane

• Contains lipids, carbohydrates, and functional
  proteins
• Double layer of phospholipid molecules
• hydrophilic headstoward watery environment, both
  sides
• hydrophobic fatty-acid tailsinside membrane
• barrier to ions and water soluble compounds

10
6 Functions of Membrane Proteins (1 of 2)

• Anchoring proteins (stabilizers)
• attach to inside or outside structures
• Recognition proteins (identifiers)
• label cells normal or abnormal
• Enzymes
• catalyze reactions

11
6 Functions of Membrane Proteins (2 of 2)

• Receptor proteins
• bind and respond to ligands (ions, hormones)
• Carrier proteins
• transport specific solutes through membrane
• Channels
• regulate water flow and solutes through membrane
  

12
Membrane Carbohydrates

• Proteoglycans, glycoproteins, and glycolipids
• extend outside cell membrane
• form sticky sugar coat (glycocalyx)

13
Functions of Membrane Carbohydrates

• Lubrication and protection
• Anchoring and locomotion
• Specificity in binding (receptors)
• Recognition (immune response)

14
Cytoplasm

• All materials inside the cell and outside the
  nucleus
• cytosol (fluid)
• dissolved materials
• nutrients, ions, proteins, and waste products
• organelles
• structures with specific functions

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What are cell organelles and their functions?
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Types of Organelles

• Nonmembranous organelles
• no membrane
• direct contact with cytosol
• Membranous organelles
• covered with plasma membrane
• isolated from cytosol

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Nonmembranous Organelles

• 6 types of nonmembranous organelles
• cytoskeleton
• microvilli
• centrioles
• cilia
• ribosomes
• proteasomes

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The Cytoskeleton

• Structural proteins for shape and strength

Figure 33a
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Microfilaments

• Thin filaments composed of the protein actin
• provide additional mechanical strength
• interact with proteins for consistency
• Pairs with thick filaments of myosin for muscle
  movement

20
Intermediate Filaments

• Mid-sized between microfilaments and thick
  filaments
• durable (collagen)
• strengthen cell and maintain shape
• stabilize organelles
• stabilize cell position

21
Microtubules

• Large, hollow tubes of tubulin protein
• attach to centrosome
• strengthen cell and anchor organelles
• change cell shape
• move vesicles within cell (kinesin and dynein)
• form spindle apparatus

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Microvilli

• Increase surface area for absorption
• Attach to cytoskeleton

Figure 33b
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Centrioles in the Centrosome

• Centrioles form spindle apparatus during cell
  division
• Centrosome cytoplasm surrounding centriole

Figure 34a
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Cilia Power

• Cilia move fluids across the cell surface

Figure 34b,c
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Ribosomes

• Build polypeptides in protein synthesis
• Two types
• free ribosomes in cytoplasm
• proteins for cell
• fixed ribosomes attached to ER
• proteins for secretion

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Proteasomes

• Contain enzymes (proteases)
• Disassemble damaged proteins for recycling

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Membranous Organelles

• 5 types of membranous organelles
• endoplasmic reticulum (ER)
• Golgi apparatus
• lysosomes
• peroxisomes
• mitochondria

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Endoplasmic Reticulum (ER)
Figure 35a
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Endoplasmic Reticulum (ER)

• endo within, plasm cytoplasm, reticulum
  network
• Cisternae are storage chambers within membranes

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Functions of ER

• Synthesis of proteins, carbohydrates, and lipids
• Storage of synthesized molecules and materials
• Transport of materials within the ER
• Detoxification of drugs or toxins

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Smooth Endoplasmic Reticulum (SER)

• No ribosomes attached
• Synthesizes lipids and carbohydrates
• phospholipids and cholesterol (membranes)
• steroid hormones (reproductive system)
• glycerides (storage in liver and fat cells)
• glycogen (storage in muscles)

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Rough Endoplasmic Reticulum (RER)

• Surface covered with ribosomes
• active in protein and glycoprotein synthesis
• folds polypeptides protein structures
• encloses products in transport vesicles

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Golgi Apparatus
Figure 36a
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Golgi Apparatus

• Vesicles enter forming face and exit maturing face

Functions of the Golgi Apparatus
PLAY
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Vesicles of the Golgi Apparatus

• Secretory vesicles
• modify and package products for exocytosis
• Membrane renewal vesicles
• add or remove membrane components
• Lysosomes
• carry enzymes to cytosol

36
Transport Vesicles

• Carry materials to and from Golgi apparatus

Figure 37a
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Exocytosis

• Ejects secretory products and wastes

Figure 37b
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Lysosomes

• Powerful enzyme-containing vesicles
• lyso dissolve, soma body

Figure 38
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Lysosome Structures

• Primary lysosome
• formed by Golgi and inactive enzymes
• Secondary lysosome
• lysosome fused with damaged organelle
• digestive enzymes activated
• toxic chemicals isolated

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Lysosome Functions

• Clean up inside cells
• break down large molecules
• attack bacteria
• recycle damaged organelles
• ejects wastes by exocytosis

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Autolysis

• Self-destruction of damaged cells
• auto self, lysis break
• lysosome membranes break down
• digestive enzymes released
• cell decomposes
• cellular materials recycle

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Peroxisomes

• Are enzyme-containing vesicles
• break down fatty acids, organic compounds
• produce hydrogen peroxide (H2O2)
• replicate by division

43
Membrane Flow

• A continuous exchange of membrane parts by
  vesicles
• all membranous organelles (except mitochondria)
• allows adaptation and change

44
KEY CONCEPT

• Cells basic structural and functional units of
  life
• respond to their environment
• maintain homeostasis at the cellular level
• modify structure and function over time

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Mitochondrion Structure
Figure 39a
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Mitochondrion Structure

• Have smooth outer membrane and folded inner
  membrane (cristae)
• Matrix
• fluid around cristae

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Mitochondrial Function

• Mitochondrion takes chemical energy from food
  (glucose)
• produces energy molecule ATP

Figure 39b
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Aerobic Cellular Respiration

• Aerobic metabolism (cellular respiration)
• mitochondria use oxygen to break down food and
  produce ATP

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The Reactions

• glucose oxygen ADP ? carbon dioxide water
  ATP
• Glycolysis
• glucose to pyruvic acid (in cytosol)
• Tricarboxylic acid cycle (TCA cycle)
• pyruvic acid to CO2 (in matrix)

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KEY CONCEPT

• Mitochondria provide cells with energy for life
• require oxygen and organic substrates
• generate carbon dioxide and ATP

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How does the nucleus control the cell?
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The Nucleus

• Is the cells control center

Figure 310a
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Structure of the Nucleus

• Nucleus
• largest organelle
• Nuclear envelope
• double membrane around the nucleus
• Perinuclear space
• between 2 layers of nuclear envelope
• Nuclear pores
• communication passages

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Within the Nucleus

• DNA
• all information to build and run organisms
• Nucleoplasm
• fluid containing ions, enzymes, nucleotides, and
  some RNA
• Nuclear matrix
• support filaments

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Nucleoli in Nucleus

• Are related to protein production
• Are made of RNA, enzymes, and histones
• Synthesize rRNA and ribosomal subunits

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Organization of DNA

• Nucleosomes
• DNA coiled around histones
• Chromatin
• loosely coiled DNA (cells not dividing)
• Chromosomes
• tightly coiled DNA (cells dividing)

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What is genetic code?
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DNA and Genes

• DNA
• instructions for every protein in the body
• Gene
• DNA instructions for 1 protein

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Genetic Code

• The chemical language of DNA instructions
• sequence of bases (A, T, C, G)
• triplet code
• 3 bases 1 amino acid

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KEY CONCEPT

• The nucleus contains chromosomes
• Chromosomes contain DNA
• DNA stores genetic instructions for proteins
• Proteins determine cell structure and function

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How do DNA instructions become proteins?
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Protein Synthesis

• Transcription
• copies instructions from DNA to mRNA (in nucleus)
• Translation
• ribosome reads code from mRNA (in cytoplasm)
• assembles amino acids into polypeptide chain

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Protein Synthesis

• Processing
• by RER and Golgi apparatus produces protein

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mRNA Transcription

• A gene is transcribed to mRNA in 3 steps
• gene activation
• DNA to mRNA
• RNA processing

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Step 1 Gene Activation

• Uncoils DNA, removes histones
• Start (promoter) and stop codes on DNA mark
  location of gene
• coding strand is code for protein
• template strand used by RNA polymerase molecule

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Step 2 DNA to mRNA

• Enzyme RNA polymerase transcribes DNA
• binds to promoter (start) sequence
• reads DNA code for gene
• binds nucleotides to form messenger RNA (mRNA)
• mRNA duplicates DNA coding strand, uracil
  replaces thymine

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Step 3 RNA Processing

• At stop signal, mRNA detaches from DNA molecule
• code is edited (RNA processing)
• unnecessary codes (introns) removed
• good codes (exons) spliced together
• triplet of 3 nucleotides (codon) represents one
  amino acid

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Codons
Table 32
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Translation (1 of 6)

• mRNA moves
• from the nucleus
• through a nuclear pore

Figure 313
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Translation (2 of 6)

• mRNA moves
• to a ribosome in cytoplasm
• surrounded by amino acids

Figure 313 (Step 1)
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Translation (3 of 6)

• mRNA binds to ribosomal subunits
• tRNA delivers amino acids to mRNA

Figure 313 (Step 2)
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Translation (4 of 6)

• tRNA anticodon binds to mRNA codon
• 1 mRNA codon translates to 1 amino acid

Figure 313 (Step 3)
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Translation (5 of 6)

• Enzymes join amino acids with peptide bonds
• Polypeptide chain has specific sequence of amino
  acids

Figure 313 (Step 4)
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Translation (6 of 6)

• At stop codon, components separate

Protein Synthesis Sequence of Amino Acids in the
Newly Synthesized Polypeptide
PLAY
Figure 313 (Step 5)
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KEY CONCEPT

• Genes
• are functional units of DNA
• contain instructions for 1 or more proteins
• Protein synthesis requires
• several enzymes
• ribosomes
• 3 types of RNA

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KEY CONCEPT

• Mutation is a change in the nucleotide sequence
  of a gene
• can change gene function
• Causes
• exposure to chemicals
• exposure to radiation
• mistakes during DNA replication

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Overcoming the Cell Barrier

• The cell membrane is semipermeable
• nutrients must get in
• products and wastes must get out

78
Permeability

• Permeability determines what moves in and out of
  a cell
• A membrane that
• lets nothing in or out is impermeable
• lets anything pass is freely permeable
• restricts movement is selectively permeable

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Selective Permeability

• Cell membrane is selectively permeable
• allows some materials to move freely
• restricts other materials

Membrane Transport Fat- and Water-Soluble
Molecules
PLAY
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Restricted Materials

• Selective permeability restricts materials based
  on
• size
• electrical charge
• molecular shape
• lipid solubility

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Transport

• Transport through a cell membrane can be
• active (requiring energy and ATP)
• passive (no energy required)

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3 Categories of Transport

• Diffusion (passive)
• Carrier-mediated transport (passive or active)
• Vesicular transport (active)

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Solutions

• All molecules are constantly in motion
• Molecules in solution move randomly
• Random motion causes mixing

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Concentration Gradient

• Concentration is the amount of solute in a
  solvent
• Concentration gradient
• more solute in 1 part of a solvent than another

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Function of Concentration Gradient

• Diffusion
• molecules mix randomly
• solute spreads through solvent
• eliminates concentration gradient

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Diffusion

• Solutes move down a concentration gradient

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Factors Affecting Diffusion Rates

• Distance the particle has to move
• Molecule size
• smaller is faster
• Temperature
• more heat, faster motion

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Factors Affecting Diffusion Rates

• Gradient size
• the difference between high and low concentration
• Electrical forces
• opposites attract, like charges repel

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Diffusion and the Cell Membrane

• Diffusion can be simple or channel-mediated

Figure 315
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Simple Diffusion

• Materials which diffuse through cell membrane
• lipid-soluble compounds (alcohols, fatty acids,
  and steroids)
• dissolved gases (oxygen and carbon dioxide)

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Channel-Mediated Diffusion

• Materials which pass through transmembrane
  proteins (channels)
• are water soluble compounds
• are ions

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Factors in Channel-Mediated Diffusion

• Passage depends on
• size
• charge
• interaction with the channel

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Osmosis

• Osmosis is the diffusion of water across the cell
  membrane

Figure 316
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How Osmosis Works

• More solute molecules, lower concentration of
  water molecules
• Membrane must be freely permeable to water,
  selectively permeable to solutes

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Osmosis Water Movement

• Water molecules diffuse across membrane toward
  solution with more solutes
• Volume increases on the side with more solutes

96
Osmotic Pressure

• Is the force of a concentration gradient of water
• Equals the force (hydrostatic pressure) needed to
  block osmosis

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Tonicity

• The osmotic effect of a solute on a cell
• 2 fluids may have equal osmolarity, but different
  tonicity

Figure 317a
98
Isotonic Solutions

• A solution that does not cause osmotic flow of
  water in or out of a cell
• iso same, tonos tension

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Hypotonic Solutions

• hypo below
• Has less solutes
• Loses water through osmosis

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Cells and Hypotonic Solutions

• A cell in a hypotonic solution
• gains water
• ruptures (hemolysis of red blood cells)

Figure 317b
101
Hypertonic Solutions

• hyper above
• Has more solutes
• Gains water by osmosis

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Cells and Hypertonic Solutions

• A cell in a hypertonic solution
• loses water
• shrinks (crenation of red blood cells)

Figure 317c
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KEY CONCEPT (1 of 2)

• Concentration gradients tend to even out
• In the absence of membrane, diffusion eliminates
  concentration gradients

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KEY CONCEPT (2 of 2)

• When different solute concentrations exist on
  either side of a selectively permeable membrane,
  osmosis moves water through the membrane to
  equalize the concentration gradients

105
Special transport mechanisms
106
Special Transport Mechanisms

• Carrier-mediated transport of ions and organic
  substrates
• facilitated diffusion
• active transport

107
Characteristics of Carrier-Mediated Transport

• Specificity
• 1 transport protein, 1 set of substrates
• Saturation limits
• rate depends on transport proteins, not substrate
• Regulation
• cofactors such as hormones

108
Special Transport Mechanisms

• Cotransport
• 2 substances move in the same direction at the
  same time
• Countertransport
• 1 substance moves in while another moves out

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Facilitated Diffusion

• Passive
• Carrier mediated

Figure 318
110
How Facilitated Diffusion Works

• Carrier proteins transport molecules too large to
  fit through channel proteins (glucose, amino
  acids)
• molecule binds to receptor site on carrier
  protein
• protein changes shape, molecules pass through
• receptor site is specific to certain molecules

111
Active Transport

• Active transport proteins
• move substrates against concentration gradient
• require energy, such as ATP
• ion pumps move ions (Na, K, Ca, Mg2)
• exchange pump countertransports 2 ions at the
  same time

112
Sodium-Potassium Exchange Pump
Figure 319
113
Receptor-Mediated Endocytosis

• Receptors (glycoproteins) bind target molecules
  (ligands)
• Coated vesicle (endosome) carries ligands and
  receptors into the cell

114
Pinocytosis

• Pinocytosis (cell drinking)
• Endosomes drink extracellular fluid

Figure 322a
115
Phagocytosis

• Phagocytosis (cell eating)
• pseudopodia (psuedo false, podia feet)
• engulf large objects in phagosomes

Figure 322b
116
Exocytosis

• Is the reverse of endocytosis

Figure 37b
117
Summary

• The 7 methods of transport

Table 33
118
What is transmembrane potential?
119
Electrical Charge

• Inside cell membrane is slightly negative,
  outside is slightly positive
• Unequal charge across the cell membrane is
  transmembrane potential
• Resting potential ranges from 10 mV to 100 mV,
  depending on cell type

120
Cell Life Cycle
Figure 33
121
Cell Life Cycle

• Most of a cells life is spent in a nondividing
  state (interphase)

122
3 Stages of Cell Division

• Body (somatic) cells divide in 3 stages
• DNA replication duplicates genetic material
  exactly
• Mitosis divides genetic material equally
• Cytokinesis divides cytoplasm and organelles into
  2 daughter cells

123
Interphase

• The nondividing period
• G-zero phasespecialized cell functions only
• G1 phasecell growth, organelle duplication,
  protein synthesis
• S phaseDNA replication and histone synthesis
• G2 phasefinishes protein synthesis and centriole
  replication

124
DNA Replication

• DNA strands unwind
• DNA polymerase attaches complementary nucleotides

Figure 324
125
Mitosis

• Mitosis divides duplicated DNA into 2 sets of
  chromosomes
• DNA coils tightly into chromatids
• chromatids connect at a centromere
• protein complex around centromere is kinetochore

126
Features of Prophase

• Nucleoli disappear
• Centriole pairs move to cell poles
• Microtubules extend between centriole
  pairs
• Nuclear envelope disappears
• Spindle fibers attach to kinetochore

127
Features of Metaphase

• Chromosomes align in a central plane (metaphase
  plate)

128
Features of Anaphase

• Microtubules pull chromosomes apart
• Daughter chromosomes groups near centrioles

129
Features of Telophase

• Nuclear membranes reform
• Chromosomes uncoil
• Nucleoli reappear
• Cell has 2 complete nuclei

130
KEY CONCEPT

• Mitosis duplicates chromosomes in the nucleus for
  cell division

131
Features of Cytokinesis

• Division of the cytoplasm
• Cleavage furrow around metaphase plate
• Membrane closes, producing daughter cells

132
Long Life, Short Life

• Muscle cells, neurons rarely divide
• Exposed cells (skin and digestive tract) live
  only days or hours
• Normally, cell division balances cell loss

133
Factors Changing Cell Division

• Increases cell division
• internal factors (MPF)
• extracellular chemical factors (growth factors)
• Decreases cell division
• repressor genes (faulty repressors cause cancers)
• worn out telomeres (terminal DNA segments)

134
Cell Differentiation

• Cells specialize or differentiate
• to form tissues (liver cells, fat cells, and
  neurons)
• by turning off all genes not needed by that cell

135
KEY CONCEPT

• All body cells, except sex cells, contain the
  same 46 chromosomes
• Differentiation depends on which genes are active
  and which are inactive

136
SUMMARY (1 of 4)

• Structures and functions of human cells
• Structures and functions of membranous and
  nonmembranous organelles

137
SUMMARY (2 of 4)

• ATP, mitochondria, and the process of aerobic
  cellular respiration
• Structures and functions of the nucleus
• control functions of nucleic acids
• structures and replication of DNA
• DNA and RNA in protein synthesis

138
SUMMARY (3 of 4)

• Structures and chemical activities of the cell
  membrane
• diffusion and osmosis
• active transport proteins
• vesicles in endocytosis and exocytosis
• electrical properties of plasma membrane

139
SUMMARY (4 of 4)

• Stages and processes of cell division
• DNA replication
• mitosis
• cytokinesis