cell structure and functionhhh.gavilan.edu/jcrocker/documents/ch04_lecture_000.pdfmicrofilaments....

Copyright © 2009 Pearson Education, Inc..

Including some materialsfrom lectures by

Gregory AhearnUniversity of North Florida

Ammended byJohn Crocker

Chapter 4

Cell Structure and Function

Copyright © 2009 Pearson Education Inc.

What Is the Cell Theory?

Tenets of Modern Cell Theory• Every living organism is made of one or more

cells• The smallest organisms are made of single

cells while multicellular organisms are made of many cells

• All cells arise from pre-existing cells


4.1 What Features Are Shared By All Cells?

Cells are the smallest unit of life.

Cells are enclosed by a plasma membrane.

Cells use DNA as a hereditary blueprint.

Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region.

Cells obtain energy and nutrients from their environment.



Cell function limits cell size.• Most cells are small (1 to 100 um in diameter)• Cells need to exchange nutrients and wastes

with the environment• No part of the cell can be far away from the

external environment.• Diffusion of molecules across cell membranes

limits the diameter of cells.• As cells get bigger, their nutrient and waste

elimination needs grow faster than the membrane area to accommodate them.



The volume of cytoplasm grows faster than the plasma membrane area.

Fig. 4-2

Copyright © 2009 Pearson Education Inc.Fig. 4-1

frog embryo

most eukaryotic cells

mitochondrion

most bacteria

virus

proteinsdiameter of DNA double helix

chicken egg

atoms1 micrometer (m) = 1/1,000,000 m1 nanometer (nm) = 1/1,000,000,000 m

1 centimeter (cm) = 1/100 m1 millimeter (mm) = 1/1,000 m

Units of measurement:1 meter (m) = 39.37 inches

adult human

tallest treesDiameter

visi

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100 m

10 m

1 m

10 cm

1 cm

1 mm

100 m

10 m

1 m

100 nm

10 nm

1 nm

0.1 nm

Relative sizes


All Cells Share Common Features

A plasma membrane encloses all cells and regulates material flow

Cytoplasm is the fluid interior where a cell’s metabolic reactions occur• May contain organelles• Fluid portion (cytosol) contains water, salts,

and organic molecules


All Cells Share Common Features

All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint

All cells use RNA (ribonucleic acid) to copy DNA to make proteins

All cells obtain energy and nutrients from the environment

All cells use common building blocks to build the molecules of life


Some Cell Types Have Cell Walls

Cell walls are stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists

• Composed of polysaccharides like cellulose or chitin

• Support and protect fragile cells and are usually porous


Cell Walls

Cell walls in plants may have multiple layers

• Primary cell walls in plants are outermost• Secondary cell walls are innermost• Cell walls of adjacent cells joined by middle

lamellae


4.2 How Do Prokaryotic And Eukaryotic Cells Differ?

There are two kinds of cells.• Prokaryotic cells

• Are found only in two groups of single-celled organisms—the bacteria and archaea

• Eukaryotic cells• Are structurally more complex cells• Possess a membrane-enclosed nucleus• Probably arose from prokaryotic cells


There Are Two Basic Cell Types

Prokaryotic• Before nucleus


4.7 What Are The Features Of Prokaryotic Cells?

Prokaryotic cells are much smaller than eukaryotic cells (< 5 µm long)

Are very reproductively successful and so are more abundant

Have a simple internal structure

Surrounded by a stiff cell wall, which provides shape and protection

Can take the shape of rods, spheres, or helices


Prokaryotic Cells

No nuclear membrane or membrane-bound organelles are present

Some have internal membranes used to capture light

Cytoplasm contains ribosomes used for protein synthesis

Cytoplasm may contain food granules


Prokaryotic Cells

Single, circular chromosome of DNA

• Chromosome found coiled in an area called the nucleoid

Small rings of DNA (plasmids) are located in the cytoplasm


Prokaryotic Cells

Some bacteria are propelled by flagella

Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces

Pili and fimbriae are protein projections in some bacteria that further enhance adhesion


There Are Two Basic Cell Types

Eukaryotic• True nucleus• Includes Protist, Fungi, Plant, and

Animal cells


4.3 What Are The Main Features Of Eukaryotic Cells?

Eukaryotic cells are > 10 µm long

The cytoskeleton provides shape and organization

A variety of membrane-enclosed organelles perform specific functions


Major Features

Nucleus: contains DNA

Mitochondria: produce energy

Endoplasmic reticulum: synthesizes membrane components and lipids

Golgi apparatus: molecule sorting center

Lysosomes: digest cellular membranes or defective organelles

Microtubules: make up the cytoskeleton


Major Features

A generalized animal cell

Fig. 4-3mitochondrion

vesicle

cytoplasm

flagellum

lysosome

centrioleintermediatefilaments

Golgiapparatus

vesicle

nuclear pore

nuclear envelope

chromatin (DNA)nucleolus

nucleus

plasmamembrane

rough endoplasmicreticulum

ribosome

free ribosomesmoothendoplasmicreticulum

microtubules


Major Features

Animal and plant cells differ with regards to cell walls, chloroplasts, plastids, central vacuoles, and centrioles


Major Features

A generalized plant cell

Fig. 4-4

centralvacuole

mitochondrion

vesicle

plasmodesma

cell wall

plasmamembrane

intermediatefilaments

free ribosomeribosomes

nucleus

nucleolusnuclear porechromatinnuclearenvelope

roughendoplasmicreticulum

smoothendoplasmicreticulum

Golgiapparatus

chloroplast

microtubules(part of cytoskeleton)


4.4 What Role Does The Nucleus Play?

The nucleus is the largest organelle in the cell.• It is bounded by a nuclear envelope.• It contains granular-looking chromatin.• It contains the nucleolus.


The Nucleus

The nuclear envelope separates chromosomes from cytoplasm• Envelope is a double membrane with

nuclear pores for transport• Some smaller materials can move through

the pores, while others, such as DNA, are excluded.

• Outer membrane is studded with ribosomes


The Nucleus

The nucleus

nucleus

nuclearpores

(b) Yeast cell

nuclearenvelope

nuclearpores

nucleolus

chromatin

(a) Structure of the nucleus

Fig. 4-5


The Nucleus

The nucleus contains DNA in various configurations• Compacted chromosomes (during cell

division)• Diffuse chromatin (as DNA directs reactions

through an RNA intermediate by coding for proteins)


The Nucleus

Darker area within the nucleus called the nucleolus• Functions as the site of ribosome synthesis• Ribosomes synthesize proteins• Ribosomes are composed of RNA and

proteins


The Nucleus

Ribosome components are made at the nucleolus.• The nucleolus contains DNA, RNA, proteins,

and ribosomes in various stages of construction.

• This is the site where components of ribosomes are constructed.

• Ribosome components leave the nucleus and are assembled in the cytoplasm.


4.5 What Roles Do Membranes Play In Eukaryotic Cells?

The plasma membrane isolates the cell, and alternately, helps it interact with its environment.• The phospholipid bilayer contains globular

proteins that regulate the transport of molecules into and out of the cell.

• Plant, fungi, and some protist cells also have a cell wall outside the plasma membrane, which acts as a protective coating.


System of Membranes

The endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell• There are two forms of ER:

• Rough endoplasmic reticulum: is studded with ribosomes

• Smooth endoplasmic reticulum: has no ribosomes


System of Membranes

Smooth ER has no ribosomes• Contains enzymes that detoxify drugs (in liver

cells) • Synthesizes phospholipids and cholesterol.• Together with rough ER are the sites of new

membrane synthesis for the cell.


System of Membranes

Rough ER is studded with ribosomes on outside• Produces proteins and phospholipids destined

for other membranes or for secretion (export)• Together with rough ER are the sites of new

membrane synthesis for the cell.


System of Membranes

Vesicles are membranous sacs that transport substances among the separate regions of the membrane system


System of Membranes

The Golgi Apparatus is a set of stacked flattened sacs • Receive proteins from ER (via transport

vesicles) and sorts them by destination• Modify some molecules (e.g. proteins to

glycoproteins)• Package material into vesicles for transport


System of Membranes

Three fates of substances made in the membrane system:

1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane – The following figure illustrates this process

for antibodies– Antibodies are proteins produced by white

blood cells to inactivate foreign disease- causing agents


System of Membranes

2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell• Lysosomes fuse with food vacuoles and

digest food into basic nutrients• In the cytoplasm, they digest defective

organelles or pieces of membrane into component parts that can be recycled.


System of Membranes

3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes


4.6 What Other Structures Play Key Roles In Eurkaryotic Cells?

Vacuoles

Mitochondria

Chloroplasts

Plastids

Cytoskeleton

Cilia and flagella


Vacuoles

Fluid-filled sacs with a single membrane

Functions of vacuoles• Contractile vacuoles in freshwater organisms

used to collect and pump water out• Many plant cells have a large central vacuole.• Plant central vacuoles used in several ways

• Maintain water balance• Store hazardous wastes, nutrients, or

pigments• Provide turgor pressure on cytoplasm to

keep cells rigid


Mitochondria Extract Food Energy

Mitochondria are round, oval, or tubular sacs of double-membranes• Inner membrane is folded into cristae• Intermembrane compartment lies between

inner and outer membranes• Matrix space within inner membrane



Function as the “powerhouses of the cell”• Mitochondria extract energy from food

molecules• Extracted energy is stored in high-energy

bonds of ATP• Energy extraction process involves anaerobic

and aerobic reactions



Mitochondria may be remnants of free-living prokaryotes (endosymbiotic hypothesis)


Chloroplasts

Chloroplasts are specialized organelles surrounded by a double membrane• Outer membrane• Inner membrane encloses the stroma space

• Stacked hollow membranous sacs (grana) within stroma are called thylakoids

• The thylakoid membranes contain chlorophyll and other pigments that capture sunlight and with CO2 and water make sugar and O2 (photosynthesis)


Plants Use Plastids for Storage

Plastids found only in plants and photosynthetic protists

Surrounded by a double membrane

Functions

• Storage for photosynthetic products like starch

• Storage of pigment molecules giving color to ripe fruit


Cytoskeleton

The cytoskeleton provides shape, support, and movement.• All organelles in the cell do not float about the

cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.

Several type of protein fibers make up the cytoskeleton.• Microfilaments: thin fibers• Intermediate filaments: medium-sized fibers • Microtubules: thick fibers


Cytoskeleton

Fig. 4-9

plasma membrane

microfilaments

mitochondrion

intermediatefilaments

ribosomes

endoplasmicreticulummicrotubule

vesicle

(a) Components of the cytoskeleton (b) Cell with stained cytoskeleton

microtubules (red)

nucleus

microfilaments (blue)


Cilia and Flagella

Cilia and flagella are extensions of the plasma membrane

Cilia and flagella are composed of microtubules in a “9+2” arrangement formed by centrioles which become membrane-anchored structures called basal bodies

Cilia are short (10-25 µm) and numerous while flagella are long (50-75 µm) but few in any cell


Cilia and Flagella

Long pairs of microtubules slide along each other (using ATP) causing movement of cilia and flagella

Functions• Cilia or flagella may be used to move cell

about• Cilia may be used to create currents of moving

fluid in their environment



Cilia provide force parallel to the plasma membrane, which can be described as a “rowing” motion.

Fig. 4-10a

return stroke

cilia liningthe trachea

plasma membranepower stroke

(a) Cilium

propulsion of fluid



Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat.

flagellumof humansperm

continuous propulsion

direction of locomotion

(b) Flagellum

propulsion of fluid

Fig. 4-10b


Evolution of Membrane-Enclosed Organelles

The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago

Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis)


Evolution of Mitochondria

Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest

Predatory cell and bacterium gradually enter into a symbiotic relationship

Descendants of engulfed bacterium evolve into mitochondria


Evolution of Chloroplasts

Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium

Predatory cell and bacterium gradually enter into a symbiotic relationship

Descendants of engulfed bacterium evolve into chloroplasts


Evidence for Endosymbionts

Many biochemical features are shared by eukaryotic organelles and living bacteria

Mitochondria, chloroplasts, and centrioles contain their own supply of DNA

Living intermediates (modern cells that host bacterial endosymbionts)• Pelomyxa palustris harbors aerobic bacteria• Paramecium harbors photosynthetic bacteria

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