Lecture 1 Cell.ppt

MCAT
Prep
Exam
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor 1
Cell Structure and
Function
Prepared by Gezim Balliu

2
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

4
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

5
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

7
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

9
Microscopy Today: Immunofluorescence
Light Microscope
 Antibodies developed against a specific protein
 Fluorescent dye molecule attached to antibody
molecules
 Specimen exposed to fluorescent antibodies
 Ultra-violet light (black light) passed through
specimen
 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

10
Microscopy and Amoeba proteus

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 x-
ray 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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13
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

14
Cell Fractionation and Differential
Centrifugation

Eukaryotes Vs Prokaryotes
Eukaryotic Cells Prokaryotic Cells
The cells of “complex” organisms,
including all plants, Protists, fungi and
animals
“Simple” organisms, including
bacteria and cyanobacteria
(blue-green algae)
Contain a nucleus and membrane
bound organelles
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
Usually exist as single, virtually
identical cells
Cell Wall present in Plants and Fungi
only
Ribosome: 40s, 60S
Cell Wall
Ribosome: 30S, 50S
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16
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

19
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

20
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

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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27
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)

29
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

31
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

32
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

34
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)

36
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)

38
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

42
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

44
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

45
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

47
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

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

51
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

52
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

54
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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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

59
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

61
Comparison of Prokaryotic and
Eukaryotic Cells

Lecture 1 Cell.ppt

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