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
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
3
Sizes of Living Things
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
Surface to Volume Ratio
6
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)
7
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
8
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?
9
Transmission Electron Microscope
10
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
11
Microscopy and Amoeba proteus
12
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

14
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
15
Cell Fractionation and Differential
Centrifugation
16
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
17
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
18
The Structure of Bacteria
19
The Structure of Bacteria
20
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
21
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
22
Hypothesized Origin of Eukaryotic Cells
23
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
24
Plasma Membrane
25
Animal Cell Anatomy
26
Plant Cell Anatomy
27
Cytosole

Cytosol, contains many long, fine filaments
of protein that are responsible for cell
shape and structure and thereby form the
cell’s cytoskeleton
28
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
Anatomy of the Nucleus
30
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
Nucleus, Ribosomes, & ER
32
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
33
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

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Studded with ribosomes on cytoplasmic side
Protein anabolism

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Synthesizes proteins
Modifies and processes proteins

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Adds sugar to protein
Results in glycoproteins
Smooth ER

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
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No ribosomes
Synthesis of lipids
Site of various synthetic processes, detoxification, and storage
Forms transport vesicles
34
Endoplasmic Reticulum
35
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
Golgi Apparatus
37
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
Lysosomes
39
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.
40
Endomembrane System: A Visual Summary
41
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
Peroxisomes
43
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
Vacuoles
45
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
46
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
Chloroplast Structure
48
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
49
Mitochondrial Structure
50
Mitochondrial Origin Hypothesis
51
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

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Microfilament

Intermediate Filaments

Microtubules
Assemble and disassemble as needed
52
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

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
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For moving stuff around within cell
Cytoplasmic streaming
Function in pseudopods of amoeboid cells
Important component in muscle contraction
53
The Cytoskeleton: Actin Filament Operation
54
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
55
The Cytoskeleton: Microtubules



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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)
56
The Cytoskeleton: Microtubule Operation
57
The Cytoskeleton
58
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
Cytoskeleton: Centrioles
60
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
Structure of a Flagellum
62
Comparison of Prokaryotic and
Eukaryotic Cells
63
Lecture 1
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
MCAT Exam Prep
Membrane Structure
and Function
64
Outline

Membrane Models


Plasma Membrane Structure and Function



Phospholipids
Proteins
Plasma Membrane Permeability




Fluid-Mosaic
Diffusion
Osmosis
Transport Via Carrier Proteins
Cell Surface Modifications
65
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
66
Unit Membrane
67
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
68
The Fluid Mosaic Model
69
Transmembrane Proteins
70
Functions of Membrane Proteins

Channel Proteins:



Carrier Proteins:

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

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
71
Membrane Protein Diversity
72
Science Focus: Cell Signaling
73
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
74
Passage of Molecules Across the
Membrane
75
Types of Membrane Transport: Overview
76
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
77
Gas Exchange in Lungs: Diffusion
Across Lung
78
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
79
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
80
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
81
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
82
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)
83
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
84