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Transcript of Chapter 3 Cellular Organization
8/13/2019 Chapter 3 Cellular Organization
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The Cellular Level of
Organization
Chapter 3
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Ch 3 Outline
Plasma membrane functions
Cellular organelles- functions
Nucleus/DNA
Diffusion/osmosis
Transport mechanisms
Transmembrane potential
Cell life cycle/regulation
Cancer
Cellular differentiation
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Cell Theory
Cells are the building blocks of all life
All cells come from the division of preexisting
cells
Cells are the smallest units that perform all vital
physiological functions
Each cell maintains homeostasis at the cellular
level
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An Introduction to Cells
Sex cells (germ cells)- reproductive cells
Male sperm
Female oocyte (egg)
Somatic cells (soma = body)
All body cells except sex cells
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An Introduction to Cells
All cells are surrounded by a extracellular fluid(interstitial fluid)
Plasma membrane (cell membrane) separates
cytoplasm from the extracellular fluid
Cytoplasm- cell contents
Cytosol- liquid within cell
Organelles- intracellular structures
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Anatomy of a Model Cell
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Plasma Membrane
Functions of the Plasma Membrane Phys ical iso lat ion - barrier
Maintain homeostasis within cell
Regu lates exchange with environment
Ions and nutrients enter
Wastes eliminated and cellular products released
Monitors the environment
Extracellular fluid composition- pH, composition, concentration
Chemical signals- activation/deactivation
Structural suppo rt
Anchors cells and tissues
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Plasma Membrane
Double layer of phospholipid molecules Hydrophilic heads- toward watery environment,
both sides
Hydrophobic fatty-acid tails- inside membrane Barrier to ions and water —soluble compounds
Polar
Nonpolar
Polar
Nonpolar
Polar
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Plasma Membrane- Membrane Proteins
Integral proteins- within the membrane
Peripheral proteins- bound to inner or
outer surface of the membrane
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Membrane Proteins
Anchoring proteins (stabilizers)- attach to inside oroutside structures
Recognition proteins (identifiers)- label cells asnormal or abnormal
Enzymes- catalyze reactions
Receptor proteins- bind and respond to ligands(ions, hormones)
Carrier proteins- transport specific solutes throughmembrane
Channels- regulate water flow & solutes through
membrane
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Membrane Carbohydrates
Proteoglycans, glycoproteins, glycolipids Extend outside cell membrane
Form sticky ―sugar coat‖ -glycocalyx
Functions of the glycocalyx
Lubrication & protection
Anchoring & locomotion Specificity in binding (receptors)
Recognition (immune response)
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Plasma Membrane
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Organelles and the Cytoplasm
All materials inside cell & outside nucleus(thick syrupy consistency, lots of proteins)
Cytosol (fluid)
Dissolved materials: – nutrients, ions, proteins, and waste products
High potassium/low sodium
High protein
High carbohydrate/low amino acid and fat
Organelles
Structures with specific functions
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Organelles
Nonmembranous organelles- no membrane
Direct contact with cytosol
Includes cytoskeleton, microvilli, centrioles, cilia,
ribosomes, proteasomes
Membranous organelles- covered with plasma
membrane
Isolated from cytosol
Includes endoplasmic reticulum (ER), the Golgi
apparatus, lysosomes, peroxisomes, mitochondria
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Cytoskeleton
Structural
proteins for shape
and strength
Microfilaments
Intermediate
filaments
Microtubules
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Cytoskeleton- Microfilaments
Microfilaments- thin filaments composed ofthe protein actin
Common in periphery of cell
Functions:
Anchor cytoskeleton to plasma membrane
Determine consistency of cytoplasm
Pair with thick filaments of myosin for movement
in muscle
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Cytoskeleton- Intermediate Filaments
Intermediate filaments- mid-sized betweenmicrofilaments and thick filaments
Most durable (collagen)
Functions:
Strengthen cell and maintain shape Stabilize organelles
Stabilize cell position with respect to surrounding cells
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Cytoskeleton- Microtubules
Microtubules- large, hollow tubes of tubulin protein
Extend outward into periphery from centrosome
Form primary components of cytoskeleton Functions:
Strengthen cell and anchor organelles
Change cell shape
Move vesicles within cell (kinesin and dynein)
Form spindle apparatus
Form structural components of cilia, centrioles
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Microtubules
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Microvilli
-Increase surface area forabsorption
-Attach to cytoskeleton
Actin filaments
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Centrioles
Centrioles in the Centrosome:
-Form spindle apparatus during cell
division
-Centrosome: cytoplasm surrounding
centriole
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Cilia
Cilia- small hair-like extensions
Cilia move fluids across the cell surface
Respiratory tract, reproductive tract
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Ribosomes
Build polypeptides in protein synthesis Free ribosomes in cytoplasm- manufacture
proteins for cell
Fixed ribosomes attached to ER- manufactureproteins for secretion
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Proteasomes
Contain enzymes (proteases) Disassemble damaged proteins for
recycling
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Membranous Organelles
Five types of membranous organelles
Endoplasmic reticulum (ER)
Golgi apparatus
Lysosomes
Peroxisomes
Mitochondria
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Endoplasmic reticulum (ER)
Network of intracellular membranes connected
to nuclear envelop
Cisternae- storage chambers within membranes
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Endoplasmic reticulum (ER)
Smooth ER- no ribosomes
Rough ER- bound ribosomes
Functions:
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 ER
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 ER
Surface covered with ribosomes:
Active in protein and glycoprotein synthesis
Folds polypeptides protein structures
Encloses products in transport vesicles
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Rough Endoplasmic Reticulum
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Golgi Apparatus
Transport vesicles carry proteins to be excreted from
cell from ER to golgi
Vesicles enter forming face & exit maturing face
Functions:
Modifies, packages secretions Renews, modifies plasma membrane
Packages special
enzymes within vesicles for
use in cytosol
cis
trans
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Functions of the Golgi Apparatus
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Golgi Apparatus
Secretory vesicles: modify
& package products for
exocytosis, secretedproducts
Membrane renewal
vesicles: add or remove
membrane components,
fuse to plasma membrane
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Lysosomes
Powerful enzyme-containing vesicles: lyso- = dissolve, soma = body
Breakdown, recycle large molecules & organelles
Primary lysosome: formed by Golgi apparatus,
inactive enzymes
Secondary lysosome: lysosome fused with
damaged organelle
Digestive enzymes activated
Toxic chemicals isolated
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Lysosomes
Functions
Clean up inside cells
Break down large molecules
Attack bacteria
Recycle damaged organelles
Eject wastes by exocytosis
Autolysis: Auto- = self, lysis = break
Self-destruction of damaged cells:
– Lysosome membranes break down – Digestive enzymes released
– Cell decomposes
– Cellular materials recycle
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Lysosome Functions
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Peroxisomes
Produced from pre-existing peroxisomes, notgolgi apparatus like lysosomes
Enzymes produced by free ribosomes
Functions:
Break down fatty acids, organic compounds
Produce hydrogen peroxide (H2O2)
H2O2 is broken down into water and oxygen
Large number in liver- metabolically active
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Mitochondria
Smooth outer & inner
membrane withnumerous folds-cristae
Matrix- fluid around cristae
Take chemical energy
from food (glucose):produces ATP
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Mitochondria
Aerobic metabolism- cellular respiration Use oxygen to break down food & produce ATP
Glycolysis: glucose to pyruvic acid (in cytosol) Krebs Cycle: pyruvic acid to CO2 (in matrix)
Generates protons for ETC
Electron transport chain: oxidative phosphorylation,
generates ATP (inner mitochondrial membrane)
Role of Mitochondria in Energy
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Role of Mitochondria in EnergyProduction
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Nucleus
Largest organelle- cell’s control center
Nuclear envelope- double membrane around the nucleus
Perinuclear space- between 2 layers of the nuclear
envelope
Nuclear pores- communication passages
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Contents of Nucleus
DNA- all information to build and run organisms
Nucleoplasm- fluid containing ions, enzymes,
nucleotides, and some RNA
Nuclear matrix- support filaments
Nucleoli- synthesize rRNA and ribosomal subunits
Nucleosomes- DNA coiled around histones
Chromatin- loosely coiled DNA (cells not dividing)
Chromosomes- tightly coiled DNA (cells dividing)
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Nucleus
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Organization
of DNA
within theNucleus
I f ti St i th N l
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Information Storage in the Nucleus
DNA- instructions for every protein in the body
Gene- DNA instructions for one protein
Genetic code- chemical language of DNA
instructions:
Sequence of bases (A, T, C, G)
Triplet code: 3 bases = 1 amino acid
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P t i S th i
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Protein Synthesis
Role of Gene Activation in Protein Synthesis
Nucleus contains chromosomes
Chromosomes contain DNA
DNA stores genetic instructions for proteins
Proteins determine cell structure and function
P t i S th i
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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
Processing By RER and Golgi apparatus produce protein
T i ti f RNA
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Transcription of mRNA
A gene is transcribed to mRNA in threesteps
Gene activation
DNA to mRNA
RNA processing
T i ti f RNA
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Transcription of mRNA
Step 1: Gene activation Uncoils DNA, removes
histones
Start (promoter ) & stop
codes on DNA marklocation of gene:
Coding strand is code for
protein
Template strand used by
RNA polymerase molecule
T i ti f RNA
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Transcription of mRNA
Step 2: DNA to mRNA
Enzyme RNA polymerase
transcribes DNA:
Binds to promoter Reads DNA code for gene
Binds nucleotides, forming
messenger RNA (mRNA)
mRNA duplicates DNA coding
strand, uracil replaces thymine
T i ti f RNA
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Transcription of mRNA
Step 3: RNA processing
At stop signal, mRNA detaches
from DNA molecule:
Code is edited- RNA processing Introns removed (non-coding)
Exons spliced together
Codon (3 nucleotides)
represents 1 amino acid
mRNA Transcription
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mRNA Transcription
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Protein Synthesis
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Protein Synthesis
Translation
tRNA anticodon binds to mRNA codon
1 mRNA codon translates to 1 amino acid
Enzymes join amino acids with peptide bonds
Polypeptide chain has specific sequence of aminoacids
At stop codon, components separate
Process of Translation
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Process of Translation
Process of Translation
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Process of Translation
Process of Translation
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Process of Translation
Protein Synthesis
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Protein Synthesis
Nucleus Controls Cell Structure
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& Function
Direct control through synthesis of
Structural proteins (cytoskeleton, receptors)
Secretions
Alter internal structure of cell, sensitivity to
substances in environment, secretory functions
Indirect control over metabolism through
enzymes
Membrane Transport
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Membrane Transport
Plasma membrane- barrier
Nutrients must get in
Products and wastes must get out
Permeability determines what moves in and outof a cell
Membrane that
Lets nothing in or out- impermeable Lets anything pass- freely permeable
Restricts movement- selectively permeable
Membrane Transport
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Membrane Transport
Plasma membrane- selectively permeable Allows some materials to move freely
Restricts other materials
Selective permeability restricts materials based
on
Size
Electrical charge
Molecular shape
Lipid solubility
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Membrane Transport Diffusion
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Membrane Transport- Diffusion
All molecules are constantly in motion Molecules in solution move randomly
Random motion causes mixing
Concentration- amount of solute in a solvent
Concentration gradient- more solute in one
part of a solvent than another Diffusion is a function of the concentration gradient
Diffusion
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Diffusion
Molecules mix randomly
Solute spreads through solvent
Eliminates concentration gradient
Solutes move down a concentration gradient
Factors Affecting Diffusion
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Factors Affecting Diffusion
Distance the particle has to move
Molecule size- smaller is faster
Temperature- more heat, faster motion
Gradient size- difference between high & low
concentrations
Electrical forces- opposites attract, like
charges repel
Diffusion Across Plasma Membranes
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Diffusion Across Plasma Membranes
Can be simple or channel mediated
Simple diffusion: through plasma membrane
Lipid-soluble compounds- alcohols, fatty acids,
steroids
Dissolved gases- oxygen, carbon dioxide
Transmembrane proteins: pass through channels
Water-soluble compounds
Ions- have a charge
Diffusion Across Plasma Membranes
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Diffusion Across Plasma Membranes
Factors in channel-mediated diffusion
Passage depends on:
Size
Charge
Interaction with the channel
Diffusion Across Plasma Membrane
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Diffusion Across Plasma Membrane
Osmosis: A Special Case of Diffusion
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Osmosis: A Special Case of Diffusion
Osmosis- the diffusion of water across cell
membrane
More solute molecules, lower concentration of
water molecules
Membrane must be freely permeable to water,selectively permeable to solutes
Water molecules diffuse across membrane
toward solution with more solutes Volume increases on the side with more solutes
Osmosis
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Osmosis
Osmosis
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Osmosis
Osmotic Pressure Force of a
concentration
gradient of water
Equals the force
(hydrostatic pressure)
needed to blockosmosis
Osmolarity and Tonicity
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Osmolarity and Tonicity
The osmotic effect of a solute on a cell:
Two fluids may have equal osmolarity, but
different tonicity
Isotonic (iso- = same, tonos = tension)
A solution that does not cause osmotic flow ofwater in or out of a cell
Hypotonic (hypo- = below)
Has less solutes & loses water through osmosis
Hypertonic (hyper- = above)
Has more solutes and gains water by osmosis
Osmolarity and Tonicity
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Osmolarity and Tonicity
A cell in a hypotonic solution: Gains water
Ruptures (hemolysis of red blood cells)
A cell in a hypertonic solution:
Loses water
Shrinks (crenation of red blood cells)
Osmotic Flow across a
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Plasma Membrane
Carrier-Mediated Transport
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Carrier Mediated Transport
Carrier-mediated transport of ions & organic
substrates
Facilitated diffusion (passive)
Active transport
Characteristics: Specificity:
One transport protein, one set of substrates
Saturation limits: Rate depends on transport proteins, not substrate
Regulation:
Cofactors such as hormones
Carrier-Mediated Transport
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Carrier Mediated Transport
Cotransport (symport)- two substances move in
the same direction at the same time
Countertransport (antiport)- one substance
moves in while another moves out
Carrier-Mediated Transport
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Carrier Mediated Transport
Facilitated diffusion- passive
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
Facilitated Diffusion
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Facilitated Diffusion
Carrier-Mediated Transport
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Carrier Mediated Transport
Active transport Active transport proteins:
Move substrates against concentration gradient
Require energy, such as ATP
Ion pumps move ions (Na+, K+, Ca2+, Mg2+)
Exchange pump countertransports 2 ions at the
same time
Active Transport
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Active Transport
Sodium-potassiumexchange pump
Active transport,
carrier mediated:
Sodium ions (Na+)
out, potassium ions
(K+) in
1 ATP moves 3 Na+
and 2 K+
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Vesicular Transport
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Vesicular Transport
Bulk transport- materials move into or out of cell in
vesicles
Endocytosis (endo- inside)- active transport using
ATP:
Receptor mediated
Pinocytosis
Phagocytosis
Exocytosis (exo- outside)
Granules or droplets are released from the cell
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Receptor-Mediated Endocytosis
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p y
Pinocytosis
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y
Endosomes ―drink‖ extracellular fluid
Phagocytosis
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g y
Pseudopodia
psuedo- false
pod- foot
Engulf large objects in
phagosomes
Exocytosis
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y
Reverse of endocytosis
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Transmembrane Potential
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Interior of cell- negative, outside- positive
Unequal charge across the plasma membrane-
transmembrane potential
Resting potential ranges: –10 mV to –100 mV,
depending on cell type
Cell Life Cycle
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y
Most of a cell’s
life is spent in
nondividing state-interphase
Cellular Life Cycle- Interphase
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y p
Nondividing period G0 phase- specialized cell functions only
(neurons, muscle cells)
G1 phase- cell growth, organelle duplication,
protein synthesis
S phase- DNA replication and histone synthesis
G2 phase- finishes protein synthesis & centriole
replication
DNA Replication- S phase
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p p
DNA strands unwind, DNA polymerase attaches
complementary nucleotides
Mitosis- Prophase
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p
Chromosomes become visible under light microscope
Nucleoli disappear
Centriole pairs move to cell poles
Microtubules (spindle fibers) extend between centriole
pairs
Nuclear envelope disappears
Spindle fibers attach to kinetochore
Interphase Early
ProphaseLate Prophase
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Prophase
Metaphase
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Chromosomes align along metaphase plate
Anaphase
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Microtubules pull sister chromatids apart
Telophase
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Nuclear membranes reform, chromosomes uncoil
Nucleoli reappear- cell has 2 complete nuclei
Cytokinesis
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y
Division of the cytoplasm
Cleavage furrow around metaphase plate
Membrane closes, producing daughter cells
Cell Differentiation
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All cells carry complete DNA instructions for allbody functions- don’t look the same!
Cells differentiate- become specialized
Form distinct cell types (liver cells, fat cells, neurons) Turn off all genes not needed by that cell
All body cells, except sex cells, contain the same
46 chromosomes
Differentiation depends on which genes are