Chapter 3

Cell Structure and Function

Video

The Cellular Level of Organization

•  The cell is the structural and functional unit of an organism.

•  Smallest structure capable of performing all the functions necessary for life.

The Cell Theory

•  All organisms are composed of one or more cells.

•  Cells are the basic living unit of structure and function in organisms.

•  All cells come only from other cells.

•  Most cells are microscopic – Cells vary in size and shape

Human height

Length of some nerve and muscle cells

Chicken egg

Frog egg

Una

ided

eye

Ligh

t mic

rosc

ope

Ele

ctro

n m

icro

scop

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10 m

1 m

100 mm (10 cm)

10 mm (1 cm)

1 mm

100 µm

10 µm

1 µm

100 nm

10 nm

1 nm

0.1 nm Atoms

Proteins

Small molecules

Lipids

Viruses

Ribosome

Nucleus

Mycoplasmas (smallest bacteria)

Most plant and animal cells

Most bacteria

Mitochondrion

Cells are small

Cells are limited by the Surface / Volume Ratio

•  All three have the same volume, but the group on the right has four times the surface area.

One 4-cm cube Eight 2-cm cubes Sixty-four 1-cm cubes •  All cells are surrounded by a plasma

membrane. •  The material inside of a cell is the cytoplasm. •  The plasma membrane regulates what enters

and exits a cell.

protein molecules

phospholipid bilayer

The Cell Membrane

The Cellular Level of Organization

•  Prokaryotic cells lack membrane-enclosed structures.

•  Eukaryotic cells possess membrane-enclosed structures.

Prokaryotic Cells

•  Lack a membrane-bounded nucleus – Eukaryotic cells have a nucleus

•  Domain Bacteria and Archaea •  Generally unicellular

– May be single, strings or clusters •  Not all bacteria cause disease

– Some are beneficial

•  Cell Wall –  Peptidoglycan

•  Capsule –  Or slime layer

•  Flagellum –  Movement

•  Fimbriae –  Attachment

•  Nucleoid –  NO membrane –  Single chromosome

•  Ribosomes –  Protein synthesis

Fimbriae: hairlike bristles that allow adhesion to surfaces

Flagellum: rotating filament present in some bacteria that pushes the cell forward

Ribosome: site of protein synthesis

Nucleoid: location of the bacterial chromosome

Plasma membrane: sheath around cytoplasm that regulates entrance and exit of molecules

Cell wall: covering that supports , shapes, and protects cell

Capsule: gel-like coating outside cell wall

Prokaryotic Cells Eukaryotic Cells

•  Eukaryotic cells: – Are structurally complex

– Have a nucleus

– Possess membrane-bound organelles

– Animals, plants, fungi and protists

Cytoskeleton:

Actin filaments

Nucleus:

Rough ER

Ribosomes

Golgi apparatus

Centrioles*

Cytoplasm Peroxisome

*not in plant cells

Intermediate filaments Smooth ER

Endoplasmic Reticulum: Microtubules

Centrosome

Mitochondrion

Polyribosome

Nucleolus Chromatin Nuclear envelope

Lysosome*

Vesicle

Animal Cell Central vacuole*

Smooth ER

Cytoplasm

*not in animal cells Cell wall*

Cell wall of adjacent cell

Chloroplast*

Mitochondrion

Microtubules

Plasma membrane

Actin filaments

Granum*

Ribosomes

Rough ER

Endoplasmic Reticulum:

Centrosome

Nucleus: Nuclear envelope

Chromatin Nuclear pore

Golgi apparatus Peroxisome

Nucleolus

Plant Cell

nuclear pore

Nuclear envelope: inner membrane outer membrane chromatin

nucleoplasm

nucleolus

phospholipid

nuclear pore

nuclear envelope

Stores DNA Chromatin DNA associated with proteins Nucleolus

Where ribosomal RNA (rRNA) made

Nuclear Envelope Nuclear pores

The Nucleus Ribosomes

•  Site of protein synthesis – Use messenger RNA (mRNA) as template

•  Two subunits (large and small) –  Subunits consist of rRNA and protein molecules

•  Found attached to endoplasmic reticulum or free in cytoplasm

Nucleus Chromatin

Nucleolus

Pore

Ribosomes

Rough endoplasmic reticulum

Two membranes of nuclear envelope

Endomembrane System

•  Consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, and several vesicles (tiny membranous sacs)

•  Essentially the transportation and product-processing section of the cell

•  Compartmentalizes cell

Endoplasmic Reticulum

nuclear envelope ribosomes

0.08 µm

rough endoplasmic

reticulum

smooth endoplasmic

reticulum

•  Rough ER: Studded with ribosomes, Processing and modification of proteins

•  Smooth ER: No ribosomes, synthesizes phospholipids, various other functions

Golgi Apparatus

•  Post office of the cell •  Collects, sorts, packages, and distributes

materials such as proteins and lipids •  Proteins made in RER have tags that

serve as “zip codes” to direct Golgi apparatus where to send them

Golgi apparatus

TEM

130

,000×

Transport vesicle from the Golgi

“Shipping” side of Golgi apparatus

Golgi apparatus

“Receiving” side of Golgi apparatus

Transport vesicle from ER

New vesicle forming

plasma membrane

secretion

enzyme

lysosome contains digestive enzymes that break down worn-out cell parts or substances entering the cell at the plasma membrane

secretory vesicle fuses with the plasma membrane as secretion occurs

Golgi apparatus modifies lipids and proteins from the ER; sorts them and pack ages them in vesicles

transport vesicle shuttles lipids to various locations such as the Golgi apparatus

lipid

transport vesicle shuttles proteins to various locations such as the Golgi apparatus

protein

ribosome

rough endoplasmic reticulum folds and processes proteins and pack ages them in vesicles; vesicles commonly go to the Golgi apparatus

Nucleus

smooth endoplasmic reticulum synthesizes lipids and also per forms various other functions

incoming vesicle brings substances into the cell that are digested when the vesicle fuses with a lysosome

Intra-Cellular Transport

Lysosomes

•  Produced by Golgi apparatus •  Contain hydrolytic digestive enzymes •  Garbage disposals of the cell •  Break down unwanted, foreign substances

or worn- out parts of cells

Vacuoles

•  Large membranous sacs

•  Larger than vacuole •  Most prominent in

plants •  Store substances.

– Water – Pigments – Toxins

Peroxisomes •  Membrane bound

vesicles containing enzymes

•  Break down molecules producing hydrogen peroxide

•  Immediately broken down into water and oxygen

peroxisome

© EM Research Services, Newcastle University

Energy-Converting Organelles

carbohydrate (high chemical energy)

chloroplast mitochondrion

usable energy

for cells CO2 + H2O (low chemical energy)

solar energy

ATP

Photosynthesis

–  Only plants, algae, and cyanobacteria –  Solar energy is the ultimate source of energy for most

cells

Cellular respiration

–  All organisms convert chemical energy into ATP –  ATP used for all energy-requiring processes in cells

solar energy + carbon dioxide + water carbohydrate + oxygen

carbohydrate + oxygen carbon dioxide + water + energy

grana thylakoid stroma a.

b.

double membrane

outer membrane inner membrane

thylakoid space

•  Site of Photosynthesis •  Structure:

–  Double-membrane –  Stroma –  Grana – stacks of

thylakoids

•  Single circular DNA molecule –  Make some but not all of its

own proteins –  Ribosomes

Chloroplasts

cristae matrix a.

b.

double membrane

outer membrane inner membrane

Mitochondria

•  Found in all eukaryotic cells •  Site or cellular respiration •  Structure:

– Double-membrane – Matrix – Cristae

•  Invaginations increase surface area

•  Also contain their own DNA

The Cytoskeleton

•  Maintains cell shape

•  Assists in movement of cell and organelles

•  Dynamic – assembled and dissasembled

•  Three types of protein components: – Actin Filaments –  Intermediate Filaments – Microtubules

Actin Filaments •  Two actin chains twisted in helix •  Roles

–  Structural – dense web under plasma membrane –  Found in intestinal microvilli –  Formation of pseudopods

a. Actin filaments

actin subunit

Chara

Intermediate Filaments •  Intermediate in size between actin filaments and

microtubules •  Functions:

–  Support nuclear envelope –  Cell-cell junctions, such as those holding skin cells

tightly together –  Strengthens human hair

human

fibrous subunits

b. Intermediate filaments

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

b(intermediate): © K.G. Murti/Visuals Unlimited; b(humans): © Amos Morgan/Getty RF

Microtubules •  Hollow cylinders made of tubulin (α and β) •  Assembly:

– Under control of Microtubule Organizing Center (MTOC)

– Most important MTOC is centrosome

c. Microtubules

tubulin subunit

chameleon

Centrioles •  Found in centrosomes of animals •  Short cylinders with a 9 + 0 pattern of microtubule triplets

one microtubule triplet

Cilia and Flagella

•  Hairlike projections that aid in cell movement

•  In eukaryotic cells, cilia are much shorter than flagella

•  Both are membrane-bound cylinders – 9 + 2 pattern of microtubules

Flagellum shaft

Sperm

Cilia

flagellum Flagellum cross section 25 nm

The shaft of the flagellum has a ring of nine microtubule doublets anchored to a central pair of microtubules.

In the presence of ATP, the dynein side arms reach out to their neighbors, and bending occurs.

ATP

dynein side arms

The side arms of each doublet are composed of dynein, a motor molecule.

dynein side arm

central microtubules

radial spoke

outer microtubule doublet

plasma membrane

Cilia and Flagella

DNA Original prokaryotic cell

1. Cell gains a nucleus by the plasma membrane invaginating and surrounding the DNA with a double membrane.

2. Cell gains an endomembrane system by proliferation of membrane.

3. Cell gains mitochondria.

protomitochondrion

mitochondrion

Plant cell has both mitochondria and chloroplasts.

Animal cell has mitochondria, but not chloroplasts.

protochloroplast chloroplast

4. Cell gains chloroplasts.

Endosymbiotic Theory