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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
e
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