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Anatomy and Physiology, Seventh Edition

Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

Chapter 03Chapter 03

Lecture OutlineLecture Outline**

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Chapter 3

Cell Structure and Function

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• Basic Structure of the Cell – Plasma membrane – Cytoplasm containing organelles – Nucleus

• Functions of the Cell– Basic unit of life– Protection and support through production and secretion of

various kinds of molecules– Movement. Various kinds occur because of specialized

proteins produced in the cell– Communication. Cells produce and receive electrical and

chemical signals– Cell metabolism and energy release– Inheritance. Each cell contains DNA. Some cells are

specialized to gametes for exchange during sexual intercourse

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Plasma Membrane• Separation of intracellular

vs. extracellular materials• Production of charge

difference (membrane potential) across the membrane by regulation of intracellular and extracellular ion concentrations– Outside of membrane

positively charged compared to inside because of gathering ions along outside and inside

• Glycocalyx: combinations of carbohydrates and lipids (glycolipids) and proteins (glycoproteins) on outer surface.

• Fluid-mosaic model

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Membrane Lipids• Phospholipids and cholesterol

predominate– Phospholipids: bilayer. Polar

heads facing water in the interior and exterior of the cell (hydrophilic); nonpolar tails facing each other on the interior of the membrane (hydrophobic)

– Cholesterol: interspersed among phospholipids. Amount determines fluid nature of the membrane

• Fluid nature provides/allows – Distribution of molecules within

the membrane– Phospholipids automatically

reassembled if membrane is damaged

– Membranes can fuse with each other

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Membrane Proteins

• Integral or intrinsic – Extend deeply into

membrane, often extending from one surface to the other

– Can form channels through the membrane

• Peripheral or extrinsic– Attached to integral

proteins at either the inner or outer surfaces of the lipid bilayer

• Functioning depends on 3-D shape and chemical characteristics. Markers, attachment sites, channels, receptors, enzymes, or carriers.

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Marker Molecules: Glycoproteins and Glycolipids

• Allow cells to identify one another or other molecules – Immunity

– Recognition of oocyte by sperm cell

– Intercellular communication

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Attachment Sites

• Integrins, membrane-bound proteins

• Attachment sites to other cells or to extra/intracellular molecules.

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Channel Proteins (Integral): hydrophilic region faces inward; charge determines molecules that can pass through

• Nongated ion channels: always open– Responsible for the

permeability of the plasma membrane to ions when the plasma membrane is at rest

• Gated ion channels can be open or closed– Ligand gated ion channel:

open in response to small molecules that bind to proteins or glycoproteins

– Voltage-gated ion channel: open when there is a change in charge across the plasma membrane

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Receptor Molecules

• Proteins in membranes with an exposed receptor site

• Can attach to specific ligand molecules and act as an intercellular communication system

• Ligand can attach only to cells with that specific receptor

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Receptors Linked to Channel Proteins

• Receptor molecules linked to channel proteins

• Attachment of receptor-specific ligands (e.g., acetylcholine) to receptors causes change in shape of channel protein

• Channel opens or closes• Changes permeability of cell to

some substances– Cystic fibrosis: defect in genes

causes defect(s) in channel proteins

– Drugs used to alter membrane permeability through attachment to channel protein-linked receptors

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A Receptor Linked to a G Protein

• Alter activity on inner surface of plasma membrane

• Leads to intracellular chemical signals that affect cell function

• Some hormones function in this way

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Enzymes and Carrier Protein

• Enzymes: some act to catalyze reactions at outer/inner surface of plasma membrane. Surface cells of small intestine produce enzymes that digest dipeptides

• Carrier proteins: integral proteins move ions from one side of membrane to the other– Have specific binding sites– Protein change shape to transport ions or molecules

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Movement through the Plasma Membrane

• Diffusion

• Osmosis

• Filtration

• Mediated transport mechanisms– Facilitated diffusion– Active transport– Secondary active transport

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Diffusion

• Movement of solutes from an area of higher concentration to lower concentration in solution– Concentration or density gradient: difference

between two points– Viscosity: how easily a liquid flows

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Osmosis

• Diffusion of water (solvent) across a selectively permeable membrane. Water moves from an area of low concentration of solute to an area of high concentration of solute

• Osmotic pressure: force required to prevent water from moving across a membrane by osmosis

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Osmosis• Comparative terms used

to describe osmotic pressures of solutions– Isosmotic: solutions

with the same concentrations of solute particles

– Solution with a greater concentration of solute is hyperosmotic

– Solution with a lesser concentration of solute is hyposmotic

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Osmosis and Cells

• Important because large volume changes caused by water movement disrupt normal cell function

• Cell shrinkage or swelling– Isotonic: cell neither shrinks nor swells– Hypertonic: cell shrinks (crenation)– Hypotonic: cell swells (lysis)

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Filtration

• Works like a sieve• Depends on pressure difference on either side

of a partition• Moves from side of greater pressure to lower• Example: urine formation in the kidneys.

Water and small molecules move through the membrane while large molecules remain in the blood

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Mediated Transport Mechanisms

• Involve carrier proteins or channels in the cell membrane

• Characteristics– Specificity for a single type

of molecule

– Competition among molecules of similar shape

– Saturation: rate of transport limited to number of available carrier proteins

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Saturation of a Carrier Protein

1. When the concentration of x molecules outside the cell is low, the transport rate is low because it is limited by the number of molecules available to be transported.

2. When more molecules are present outside the cell, as long as enough carrier proteins are available, more molecules can be transported; thus, the transport rate increases.

3. The transport rate is limited by the number of carrier proteins and the rate at which each carrier protein can transport solutes. When the number of molecules outside the cell is so large that the carrier proteins are all occupied, the system is saturated and the transport rate cannot increase.

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Mediated Transport Mechanisms

• Move large, water soluble molecules or electrically charged molecules across the plasma membrane.

• Amino acids and glucose in, manufactured proteins out.– Facilitated diffusion: carrier-

or channel-mediated. Passive.

– Active transport

– Secondary active transport

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Active Transport

• Requires ATP. The use of energy allows the cell to accumulate substances

• Rate of transport depends on concentration of substrate and on concentration of ATP

• Example: Na/K exchange pump that creates electrical potentials across membranes

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Secondary Active Transport

• Ions or molecules move in same (symport) or different (antiport) direction.

• Is the movement of glucose a symporter example or an antiporter example?

• This example shows cotransport of Na+ and glucose. 1. A sodium-potassium

exchange pump maintains a concentration of Na that is higher outside the cell than inside. Active transport.

2. Na moves back into the cell by a carrier protein that also moves glucose. The concentration gradient for Na provides the energy required to move glucose against its concentration gradient.

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Endocytosis

• Internalization of substances by formation of a vesicle

• Types– Phagocytosis

– Pinocytosis

– Receptor-mediated endocytosis

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Pinocytosis and Receptor-Mediated Endocytosis

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Exocytosis

• Accumulated vesicle secretions expelled from cell• Examples

– Secretion of digestive enzymes by pancreas

– Secretion of mucous by salivary glands

– Secretion of milk by mammary glands

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Cytoplasm

• Cellular material outside nucleus but inside plasma membrane

• Composed of Cytosol, Cytoskeleton, Cytoplasmic Inclusions, Organelles

• Cytosol: fluid portion. Dissolved molecules (ions in water) and colloid (proteins in water)

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Cytoskeleton• Supports the cell but has to allow for

movements like changes in cell shape and movements of cilia

– Microtubules: hollow, made of tubulin.

• Internal scaffold, transport, cell division

– Microfilaments: actin. • Structure, support for microvilli,

contractility, movement

– Intermediate filaments: mechanical strength

• Cytoplasmic inclusions: aggregates of chemicals such as lipid droplets, melanin

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Organelles

• Small specialized structures with particular functions

• Most have membranes that separate interior of organelles from cytoplasm

• Related to specific structure and function of the cell

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Nucleus

• Membrane-bound• Nucleoplasm,

nucleolus and nuclear envelope

• Much of the DNA in a cell located here

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Chromosome Structure

• Chromatin: DNA complexed with proteins (histones)

• During cell division, chromatin condenses into pairs of chromatids called chromosomes. Each pair of chromatids is joined by a centromere

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Centrioles and Spindle Fibers• Located in

centrosome: specialized zone near nucleus

• Center of microtubule formation

• Before cell division, centrioles divide, move to ends of cell and organize spindle fibers

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Cilia• Appendages projecting

from cell surfaces• Capable of movement• Moves materials over

the cell surface

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Flagella

• Similar to cilia but longer

• Usually only one per cell

• Move the cell itself in wave-like fashion

• Example: sperm cell

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Microvilli

• Extension of plasma membrane

• Increase the cell surface area

• Normally many on each cell

• One tenth to one twentieth size of cilia

• Do not move

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Ribosomes

• Sites of protein synthesis• Composed of a large and

a small subunit• Types

– Free

– Attached (to endoplasmic reticulum)

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Endoplasmic Reticulum

• Types– Rough

• Has attached ribosomes

• Proteins produced and modified here

– Smooth• No attached ribosomes

• Manufactures lipids

• Cisternae: Interior spaces isolated from rest of cytoplasm

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Golgi Apparatus

• Modification, packaging, distribution of proteins and lipids for secretion or internal use

• Flattened membrane sacs stacked on each other

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Function of Golgi Apparatus

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Action of Lysosomes

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Peroxisomes and Proteasomes• Peroxisomes

– Smaller than lysosomes– Contain enzymes to break down fatty acids and

amino acids– Hydrogen peroxide is a by-product of

breakdown

• Proteasomes– Consist of large protein complexes– Include several enzymes that break down and

recycle proteins in cell

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Mitochondria• Major site of ATP synthesis• Membranes

– Cristae: Infoldings of inner membrane

– Matrix: Substance located in space formed by inner membrane

• Mitochondria increase in number when cell energy requirements increase.

• Mitochondria contain DNA that codes for some of the proteins needed for mitochondria production.

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Overview of Cell Metabolism

• Production of ATP necessary for life

• ATP production takes place in the cytosol (anaerobic) and mitochondria (aerobic)– Anaerobic does not require

oxygen. Results in very little ATP production.

– Aerobic requires oxygen. Results in large amount of ATP.

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Overview of Protein Synthesis

• Transcription: DNA used to form RNA

• Translation: synthesis of a protein at the ribosomes using mRNA, tRNA and rRNA

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Transcription

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Post-transcriptional Modification of mRNA

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Translation

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Regulation of Protein Synthesis

• All nucleated cells except germ cells have the full complement of DNA.

• During development, differentiation occurs and some segments of DNA are turned off in some cells while those segments remain “on” in other cells.

• During the lifetime of a cell, the rate of protein synthesis varies depending upon chemical signals that reach the cell.– Example: thyroxine from the thyroid causes cells to

increase their metabolic rate. More thyroxine, higher metabolic rate; less thyroxine, lower metabolic rate.

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Cell Life Cycle

• Interphase: phase between cell divisions– Replication of DNA– Ongoing normal cell activities

• Mitosis: series of events that leads to the production of two cells by division of a mother cell into two daughter cells. Cells are genetically identical.– Prophase– Metaphase– Anaphase– Telophase

• Cytokinesis: division of cell cytoplasm

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Mitosis

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Cellular Aspects of Aging

• Cellular clock. After a certain amount of time or certain number of cell divisions, cells die.

• Death genes. Turn on late in life, or sometimes prematurely causing cells to deteriorate and die. Apoptosis.

• DNA damage. Telomeres at ends of chromosomes TTAGGG. During replication, nucleotides are lost. Telomerase protects telomeres, enzymes seem to be lost with aging.

• Free radicals. DNA mutation caused by free radicals (atoms or molecules with an unpaired electron.

• Mitochondrial damage. Mitochondrial DNA may be more sensitive to free radicals. Loss of energy, cell death.