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PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor 1

Cell Structure and Function

Lecture 1

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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 m, 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 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

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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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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

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 onlyRibosome: 40s, 60S

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

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 ApparatusConsists of flattened, curved saccules

Resembles stack of hollow pancakes

Modifies proteins and lipidsReceives 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

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 and tubulin

Spontaneous pairing of and 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

MC

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Exam

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PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor 64

Membrane Structure and Function

Lecture 1

65

Outline

Membrane Models Fluid-Mosaic

Plasma Membrane Structure and Function Phospholipids Proteins

Plasma Membrane Permeability 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 ModelThree components:

Basic membrane referred to as phospholipid bilayer

Protein moleculesFloat around like icebergs on a seaMembrane 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 attachedCholesterol

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The Fluid Mosaic Model

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Transmembrane Proteins

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Functions of Membrane Proteins

Channel Proteins: Tubular Allow passage of molecules through membrane

Carrier Proteins: Combine with substance to be transported Assist passage of molecules through membrane

Cell Recognition Proteins: Provides unique chemical ID for cells Help body recognize foreign substances

Receptor Proteins: 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 TransportSmall moleculesCan’t get through membrane lipidsCombine with carrier proteinsFollow concentration gradient

Active TransportSmall moleculesMove against concentration gradientCombining with carrier proteinsRequires energy

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Types of Transport: Carrier Proteins

Facilitated TransportSmall moleculesCan’t get through membrane lipidsCombine with carrier proteinsFollow concentration gradient

Active TransportSmall moleculesMove against concentration gradientCombining with carrier proteinsRequires energy

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Types of Transport:Membrane-Assisted Transport

Macromolecules transported into or out of the cell inside vesiclesExocytosis – Vesicles fuse with plasma

membrane and secrete contentsEndocytosis – Cells engulf substances into

pouch which becomes a vesiclePhagocytosis – Large, solid material into vesiclePinocytosis – Liquid or small, solid particles go into

vesicleReceptor-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

Intercellular filaments between cells

Tight Junctions

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