Cell Structure and Function
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Transcript Cell Structure and Function
Lecture 1
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
MCAT Prep Exam
Cell Structure and
Function
1
Outline
Cellular Level of Organization
Cell theory
Cell size
Prokaryotic Cells
Eukaryotic Cells
Organelles
Nucleus and Ribosome
Endomembrane System
Other Vesicles and Vacuoles
Energy related organelles
Cytoskeleton
Centrioles, Cilia, and Flagella
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Cell Theory
Cell was not discovered untill the development of
Microscope
Detailed study of the cell began in the 1830s
A unifying concept in biology
States that:
All organisms are composed of cells
All cells come only from preexisting cells
Cells are the smallest structural and functional unit of
organisms
Cells carry genetic information in the form of DNA
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Sizes of Living Things
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Cell Size
Cells range in size from one millimeter down to
one micrometer
Cells need a large surface area of plasma
membrane to adequately exchange materials.
The surface-area-to-volume ratio requires that
cells be small
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Surface to Volume Ratio
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Microscopy Today: Compound Light
Microscope
Light passed through specimen
Focused by glass lenses
Max magnification about 1000X
Resolves objects separated by 0.2 mm, 500X
better than human eye
Resolution is limited by the wavelength of light
(nanometer)
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Compound Light Microscope
Diaphragm – controls
amount of light –
important for image
contrast
Coarse Adjustment Knob
– focuses the image
Fine Adjustment Knob –
finely focuses the image
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Microscopy Today: Transmission
Electron Microscope
Abbreviated T.E.M.
Uses a beam of electrons to allow 100 fold higher
magnification
Because it uses beam of electrons, its resolution is at
the atomic level (picometer)
Tissue must be fixed and sectioned
Can living specimen be examined by T.E.M?
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Transmission Electron Microscope
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Microscopy Today: Immunofluorescence
Light Microscope
Antibodies developed against a specific protein
Ultra-violet light (black light) passed through
specimen
Fluorescent dye molecule attached to antibody
molecules
Specimen exposed to fluorescent antibodies
Fluorescent dye glows in color where antigen is
located
Emitted light is focused by glass lenses onto human
retina
Allows mapping distribution of a specific protein
in cell
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Microscopy and Amoeba proteus
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Cells Under the Microscope
phase-contrast light microscope - look at
unstained living animal cells.
electron microscope - look at organelles
e.g. ribosomes.
fluorescence microscope - look at a living
cell expressing green fluorescent protein or
to do confocal microscopy.
Autoradiography
Radioactive compounds decay or transform
into other compounds or elements.
An autoradiograph is an image on an xray film or nuclear emulsion produced by
the pattern of decay emissions (e.g., beta
particles or gamma rays) from a distribution
of a radioactive substance
Autoradiography can also uses radioactive
molecule to study biochemical activity,
Protein synthesis
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Cell Fractionation and Differential
Centrifugation
Cell fractionation is the breaking apart of
cellular components
Differential centrifugation:
Allows separation of cell parts
Separated out by size & density
Works like spin cycle of washer
The faster the machine spins, the smaller
the parts that are settled out
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Cell Fractionation and Differential
Centrifugation
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Eukaryotes Vs Prokaryotes
Eukaryotic Cells
Prokaryotic Cells
The cells of “complex” organisms,
including all plants, Protists, fungi and
animals
Contain a nucleus and membrane
bound organelles
“Simple” organisms, including
bacteria and cyanobacteria
(blue-green algae)
Lack a nucleus and other
membrane-encased organelles.
Can specialize for certain functions,
such as absorbing nutrients from food
or transmitting nerve impulses;
multicellular organs and organisms
Cell Wall present in Plants and Fungi
only
Ribosome: 40s, 60S
Usually exist as single, virtually
identical cells
Cell Wall
Ribosome: 30S, 50S
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The Structure of Bacteria
Occur in three basic shapes:
Spherical coccus,
Rod-shaped bacillus,
Spiral spirillum (if rigid) or spirochete (if flexible).
Cell Envelope includes:
Plasma membrane - lipid bilayer with imbedded and peripheral
protein
Cell wall - maintains the shape of the cell
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The Structure of Bacteria
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The Structure of Bacteria
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The Structure of Bacteria Cytoplasm &
Appendages
Cytoplasm
Semifluid solution
Bounded by plasma membrane
Contains water, inorganic and organic molecules, and enzymes.
Nucleoid is a region that contains the single, circular DNA
molecule.
Plasmids are small accessory (extrachromosomal) rings of DNA
Appendages
Flagella – Provide motility
Fimbriae – small, bristle-like fibers that sprout from the cell
surface
Sex pili – rigid tubular structures used to pass DNA from cell to
cell
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Eukaryotic Cells
Domain Eukarya includes:
Protists
Fungi
Plants
Animals
Cells contain:
Membrane-bound nucleus that houses DNA
Specialized organelles
Plasma membrane
Much larger than prokaryotic cells
Some cells (e.g., plant cells) have a cell wall
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Hypothesized Origin of Eukaryotic Cells
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Eukaryotic Cells: Organelles
Eukaryotic cells are compartmentalized
They contain small structures called organelles
Perform specific functions
Isolates reactions from others
Two classes of organelles:
Endomembrane system:
Organelles that communicate with one another
Via membrane channels
Via small vesicles
Energy related organelles
Mitochondria & chloroplasts
Basically independent & self-sufficient
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Plasma Membrane
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Animal Cell Anatomy
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Plant Cell Anatomy
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Cytosole
Cytosol, contains many long, fine filaments
of protein that are responsible for cell
shape and structure and thereby form the
cell’s cytoskeleton
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Nucleus
Command center of cell, usually near center
Separated from cytoplasm by nuclear envelope
Consists of double layer of membrane
Nuclear pores permit exchange between nucleoplasm
& cytoplasm
Contains chromatin in semifluid nucleoplasm
Chromatin contains DNA of genes, and proteins
(Histones)
Condenses to form chromosomes
Chromosomes are formed during cell division
Nucleolus is a dense structure in the nucleus
Synthesize ribosome RNA (rRNA)
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Anatomy of the Nucleus
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Ribosomes
Are the site of protein synthesis in the cell
Composed of rRNA and protein
Consists of a large subunit and a small subunit
Subunits made in nucleolus
May be located:
On the endoplasmic reticulum (thereby making it
“rough”), or
Free in the cytoplasm
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Nucleus, Ribosomes, & ER
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Endomembrane System
Series of intracellular membranes that
compartmentalize the cell
Restrict enzymatic reactions to specific
compartments within cell
Consists of:
Nuclear envelope
Membranes of endoplasmic reticulum
Golgi apparatus
Vesicles
Several types
Transport materials between organelles of system
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Endomembrane System:
The Endoplasmic Reticulum
A system of membrane channels and saccules (flattened vesicles)
continuous with the outer membrane of the nuclear envelope
Rough ER
Studded with ribosomes on cytoplasmic side
Protein anabolism
Synthesizes proteins
Modifies and processes proteins
Adds sugar to protein
Results in glycoproteins
Smooth ER
No ribosomes
Synthesis of lipids
Site of various synthetic processes, detoxification, and storage
Forms transport vesicles
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Endoplasmic Reticulum
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Endomembrane System:
The Golgi Apparatus
Golgi Apparatus
Consists of flattened, curved saccules
Resembles stack of hollow pancakes
Modifies proteins and lipids
Receives vesicles from ER on cis (or inner face)
Modifies them and repackages them in vesicles
Release the vesicles from trans (or outer face)
Within cell
Export from cell (secretion, exocytosis)
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Golgi Apparatus
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Endomembrane System: Lysosomes
Membrane-bound vesicles (not in plants)
Produced by the Golgi apparatus
Contain powerful digestive enzymes and are highly
acidic
Digestion of large molecules
Recycling of cellular debris and resources
Autolysis may occur in injured or dying cell to cause apoptosis
(programmed cell death, like tadpole losing tail)
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Lysosomes
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Endomembrane System: Summary
Proteins produced in rough ER and lipids from
smooth ER are carried in vesicles to the Golgi
apparatus.
The Golgi apparatus modifies these products and
then sorts and packages them into vesicles that
go to various cell destinations.
Secretory vesicles carry products to the
membrane where exocytosis produces
secretions.
Lysosomes fuse with incoming vesicles and
digest macromolecules.
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Endomembrane System: A Visual Summary
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Peroxisomes
Similar to lysosomes
Membrane-bounded vesicles
Enclose enzymes that rid the cell of toxic peroxides
Participate in the metabolism of fatty acids and many
other metabolites
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Peroxisomes
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Vacuoles
Membranous sacs that are larger than vesicles
Store materials that occur in excess
Others very specialized (contractile vacuole)
Plants cells typically have a central vacuole
Up to 90% volume of some cells
Functions in:
Storage of water, nutrients, pigments, and waste products
Development of turgor pressure
Some functions performed by lysosomes in other eukaryotes
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Vacuoles
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Energy-Related Organelles:
Chloroplast Structure
Bounded by double membrane
Inner membrane infolded
Forms disc-like thylakoids, which are stacked to form
grana
Suspended in semi-fluid stroma
Chlorophyll
Green photosynthetic pigment
Chlorophyll capture solar energy
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Energy-Related Organelles: Chloroplasts
Serve as the site of photosynthesis
Captures light energy to drive cellular machinery
Photosynthesis
Synthesizes carbohydrates from CO2 & H2O
Makes own food using CO2 as only carbon source
Inorganic molecules (Energy-poor compounds) are converted to organic
molecules (energy-rich compounds)
Only plants, algae, and certain bacteria are capable of conducting
photosynthesis
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Chloroplast Structure
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Energy-Related Organelles: Mitochondria
Smaller than chloroplast
Contain ribosomes and their own DNA
Surrounded by a double membrane
Inner membrane surrounds the matrix and is convoluted (folds) to form
cristae.
Matrix – Inner semifluid containing respiratory enzymes
Break down carbohydrates
Involved in cellular respiration
Produce most of ATP utilized by the cell
Contain their own DNA and ribosome i.e. they are semiautonomous
Inherited from Oocyte
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Mitochondrial Structure
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Mitochondrial Origin Hypothesis
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The Cytoskeleton
Maintains cell shape
Assists in movement of cell and organelles
Aids movement of materials in and out of cells
Three types of macromolecular fibers
Microfilament
Intermediate Filaments
Microtubules
Assemble and disassemble as needed
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The Cytoskeleton: Actin Filaments
Microfilament are rods of actin
Extremely thin filaments like twisted pearl
necklace
Support for microvilli in intestinal cells
Intracellular traffic control
For moving stuff around within cell
Cytoplasmic streaming
Function in pseudopods of amoeboid cells
Important component in muscle contraction
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The Cytoskeleton: Actin Filament Operation
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The Cytoskeleton: Intermediate Filaments
Intermediate in size between actin filaments and
microtubules
Rope-like assembly of fibrous polypeptides
Functions:
Support nuclear envelope
Cell-cell junctions, like those holding skin cells tightly
together
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The Cytoskeleton: Microtubules
Hollow cylinders made of two globular proteins called
a and b tubulin
Spontaneous pairing of a and b tubulin molecules
form structures called dimers
Dimers then arrange themselves into tubular spirals
of 13 dimers around
Assembly:
Under control of Microtubule Organizing Center (MTOC)
Most important MTOC is centrosome
Function:
Provide framework for movement of organelle within cell
Direct separation of chromosomes during cell division (e.g.
Centrioles are composed of microtubules)
Provide locomotion and movement (e.g. flagella and cilia)
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The Cytoskeleton: Microtubule Operation
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The Cytoskeleton
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Microtubular Arrays: Centrioles
Short, hollow cylinders
One pair per animal cell
Located in centrosome of animal cells
Oriented at right angles to each other
Separate during mitosis to determine plane of division
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Cytoskeleton: Centrioles
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Microtubular Arrays: Cilia and Flagella
Hair-like projections from cell surface that aid in
cell movement
In eukaryotes, cilia are much shorter than flagella
Cilia move in coordinated waves like oars
Flagella move like a propeller or cork screw
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Structure of a Flagellum
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Comparison of Prokaryotic and
Eukaryotic Cells
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Lecture 1
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
MCAT Exam Prep
Membrane Structure
and Function
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Outline
Membrane Models
Plasma Membrane Structure and Function
Phospholipids
Proteins
Plasma Membrane Permeability
Fluid-Mosaic
Diffusion
Osmosis
Transport Via Carrier Proteins
Cell Surface Modifications
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Structure and Function:
The Phospholipid Bilayer
The plasma membrane is common to all cells
Separates:
Internal living cytoplasmic from
External environment of cell
Phospholipid bilayer:
External surface lined with hydrophilic polar heads
Cytoplasmic surface lined with hydrophilic polar heads
Nonpolar, hydrophobic, fatty-acid tails sandwiched in
between
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Unit Membrane
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Membrane Models
Fluid-Mosaic Model
Three components:
Basic membrane referred to as phospholipid
bilayer
Protein molecules
Float around like icebergs on a sea
Membrane proteins may be peripheral or integral
Peripheral proteins are found on the inner membrane
surface
Integral proteins are partially or wholly embedded
(transmembrane) in the membrane
Some have carbohydrate chains attached
Cholesterol
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The Fluid Mosaic Model
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Transmembrane Proteins
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Functions of Membrane Proteins
Channel Proteins:
Carrier Proteins:
Provides unique chemical ID for cells
Help body recognize foreign substances
Receptor Proteins:
Combine with substance to be transported
Assist passage of molecules through membrane
Cell Recognition Proteins:
Tubular
Allow passage of molecules through membrane
Binds with messenger molecule
Causes cell to respond to message
Enzymatic Proteins:
Carry out metabolic reactions directly
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Membrane Protein Diversity
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Science Focus: Cell Signaling
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Types of Transport: Active vs. Passive
Plasma membrane is differentially (selectively)
permeable
Allows some material to pass
Inhibits passage of other materials
Passive Transport:
No ATP requirement
Molecules follow concentration gradient
Active Transport
Requires carrier protein
Requires energy in form of ATP
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Passage of Molecules Across the
Membrane
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Types of Membrane Transport: Overview
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Types of Transport: Diffusion
A solution consists of:
A solvent (liquid), and
A solute (dissolved solid)
Diffusion
Net movement of solute molecules down a
concentration gradient
Molecules move both ways along gradient
Molecules move from high to low
Equilibrium:
When NET change stops
Solute concentration uniform – no gradient
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Gas Exchange in Lungs: Diffusion
Across Lung
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Types of Transport: Osmosis
Osmosis:
Special case of diffusion
Focuses on solvent (water) movement rather than
solute
Diffusion of water across a differentially (selectively)
permeable membrane
Solute concentration on one side high, but water
concentration low
Solute concentration on other side low, but water
concentration high
Water diffuses both ways across membrane but
solute can’t
Net movement of water is toward low water (high
solute) concentration
Osmotic pressure is the pressure that develops
due to osmosis
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Types of Transport: Carrier Proteins
Facilitated Transport
Small molecules
Can’t get through membrane lipids
Combine with carrier proteins
Follow concentration gradient
Active Transport
Small molecules
Move against concentration gradient
Combining with carrier proteins
Requires energy
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Types of Transport: Carrier Proteins
Facilitated Transport
Small molecules
Can’t get through membrane lipids
Combine with carrier proteins
Follow concentration gradient
Active Transport
Small molecules
Move against concentration gradient
Combining with carrier proteins
Requires energy
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Types of Transport:
Membrane-Assisted Transport
Macromolecules transported into or out of
the cell inside vesicles
Exocytosis – Vesicles fuse with plasma
membrane and secrete contents
Endocytosis – Cells engulf substances into
pouch which becomes a vesicle
Phagocytosis – Large, solid material into vesicle
Pinocytosis – Liquid or small, solid particles go into
vesicle
Receptor-Mediated – Specific form of pinocytosis
using a coated pit
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Cell Surface Modifications: Junctions
Cell Surfaces in Animals
Junctions Between Cells
Adhesion Junctions
Tight Junctions
Intercellular filaments between cells
Form impermeable barriers
Gap Junctions
Plasma membrane channels are joined (allows
communication)
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Cell Surface Modifications
Extracellular Matrix
External meshwork of polysaccharides and proteins
Found in close association with the cell that produced
them
Plant Cell Walls
Plants have freely permeable cell wall, with cellulose
as the main component
Plasmodesmata penetrate cell wall
Each contains a strand of cytoplasm
Allow passage of material between cells
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