Transcript Meiosis and Sexual Life Cycles (Ch. 13)

The Tour of the Cell
Chapter 6
The Fundamental Units of Life
• All living things composed of cells
• Cell structure correlated to cell function
• All cells descend from existing cells
Microscopy
• Light microscope = visible light through specimen
magnified by lenses
– Up to 1000X
• Electron microscopes (EMs)
• Scanning EM (SEM) focus beam of electrons
onto surface  3-D image
• Transmission EM (TEM)
• focus beam of electrons through specimen
•  internal structures
• Gills of fish
• HIV
yeast
Cell Fractionation
centrifuge
separates cell
components
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
Differential centrifugation
TECHNIQUE (cont.)
1000 g 10 min
Supernatant poured
into next tube
Homogenate
20,000g 20 min
Pellet
Supernatant
Nuclei, debris  mitochondria  membranes  ribosomes
80,000g 60 min
150,000g 3 hr
• Prokaryotic cells= Archaea and Bacteria
• No nucleus, no membrane-bounded organelles
• DNA in nucleoid region
0.5
µm
Eukaryotic cells = Plants, Animals, Fungi,
Protista
•DNA in nucleus
•Organelles
•Membrane bounded
•Cytoplasm = fluid + organelles
•Cytosol = fluid
Featured scientist: Robert Hooke 16351703
Micrographia was a best seller
Best CLM of its time!
The famous slide:
. . . I could exceedingly plainly
perceive it to be all perforated and
porous, much like a Honey-comb, but
that the pores of it were not regular. . .
. these pores, or cells, . . . were indeed
the first microscopical pores I ever
saw, and perhaps, that were ever
seen, for I had not met with any
Writer or Person, that had made any
mention of them before this. . .
Features of cells
1. The plasma membrane = selective barrier
allows passage of oxygen, nutrients, waste etc
• Composed of phospholipid bilayer
2. Surface to Volume ratio high
• Small cells have greater surface area relative to
volume
• Larger organisms do not have larger cells than
smaller organisms
Human
Rat
The Eukaryotic Cell
1. The Nucleus
Hela cells
A. Nuclear envelope (NE)
– Double membrane; each a bilayer
– Pores regulate entry and exit of molecules
from nucleus
Nuclear lamina
fibrous proteins maintain shape of nucleus
Lamin A and lamin B can bind histones – may have role in chromosome organization
B. Chromatin = DNA +
proteins
• Chromosomes = strands of
chromatin
C. Nucleolus
– Assembles ribosomes
• D. Nucleoplasm
– Viscous fluid of nucleus
2. Ribosomes: Protein Factories
• Assemble amino acids into polypeptides
– cytosol (free ribosomes)
– RER/NE (bound ribosomes)
3. The Endomembrane System
• Components
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Nuclear envelope
Endoplasmic reticulum (ER)
Golgi apparatus
Lysosomes
Vacuoles
*Plasma membrane
A. The Endoplasmic Reticulum
• >half of total membrane
• continuous with nuclear envelope
– Smooth ER
– lacks ribosomes
1.
2.
3.
4.
Synthesizes lipids
Metabolizes carbohydrates
Detoxifies poison
Stores calcium
• Rough ER (RER)
– Ribosomes assemble proteins  thread through ER lumen
 transport vesicles
– Membrane factory
B. The Golgi Apparatus
• flattened membranous sacs called cisternae
• cis and trans face
trans face
(“shipping” side of Golgi
apparatus)
• Functions of the Golgi apparatus:
– Modifies proteins from ER
– Sorts and packages protein into transport vesicles

Golgi makes polysaccharides in plants
Nucleus
Rough ER
Smooth ER
cis Golgi
Where do the
vesicles go?
trans Golgi
Plasma
membrane
• Virtual cell
Note: Ribosome, RER, vesicle, Golgi
C. Lysosomes
• membranous sac of enzymes that digest
macromolecules
• What do they do?
recycle cell components (autophagy)
get rid of phagocytosed invaders
form food vacuoles
How do they work?
phagocytosis A cell engulfs another cell to form a
food vacuole
– lysosome fuses with food vacuole and digests
molecules
D. Vacuoles
– Food vacuoles formed by phagocytosis
– Contractile vacuoles
• freshwater protists
• store or/and pump excess water out of cells
– Central vacuoles
• found in many plant cells
• hold organic compounds and water
4. Mitochondria
• cellular respiration generates ATP (energy)
• contain mtDNA
• all eukaryotic cells have mt
– Some have 1, some
Outer 1000s
membra
ne
Crist
ae
mitochondrion
Mitochondria
• outer membrane and inner membrane fold into
cristae
– large surface area for enzymes that synthesize ATP
5. Chloroplasts (plastid)
• found in plants and algae
• sites of photosynthesis
– green pigment chlorophyll, enzymes, other
molecules
6. Peroxisomes
• detoxify
2 H2O2
(toxic)
catalase

2H2O + O2
• Bioflix Tour of animal cell – the big picture
• Note:
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Sticky extracellular matrix
Plasma membrane
Cytoskeleton
Mitochondria- ATP, surface area
Nucleus and nuclear envelope with pores
DNA and protein wrappings, code for protein
Ribosome builds protein
Endomembrane system = RER and SER + Golgi
7. Cytoskeleton
• Network of protein fibers organize structures
and activities in cell
• Anchors organelles
• Maintains cell shape
Cytoskeleton
• interacts with motor proteins to transport cargo or for
movement
10 µm
Column of tubulin dimers
25 nm


Tubulin dimer
10 µm
Actin subunit
7 nm
5 µm
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm
• Vesicles in a plant cell
• Golgi sorting and packaging
8. Centrosomes and
Centrioles
Centrosome
Microtubule
• Centrosome
Centrioles
– microtubuleorganizing center
Longitudinal section of
one centriole
0.25 µm
Cross section
of the other centriole
– centrioles
• animal cells only
• centrosome has pair
• each with 9 triplets of microtubules arranged in a ring
centrosome
9. Cilia and Flagella
• Locomotor appendages of some cells
• Movement pattern controlled by microtubules
• Example: paramecium, algae
10. Extracellular materials
• Cells secrete materials external to plasma
membrane
• Harvard life of a cell – 3 min.
• Can you find –
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Cell membrane
Cytoskeleton
Microtubule polymerization and depolymerization
A motor protein walking along the cytoskeleton
Lysosomes and mt
A centriole
Nuclear pores with mRNA leaving nucleus
RER
Ribosomes making proteins
Vesicles budding with cis face of Golgi
Proteins leaving the cell
A. Cell Walls of Plants
Also, prokaryotes, fungi, some protists
• protects, maintains shape, prevents excessive
uptake of water
• cellulose fibers + polysaccharides and protein
• Layers of cell wall
– Primary wall: thin
– Middle lamella: between primary walls of adjacent
cells
– Secondary wall (some cells): between plasma
membrane and primary cell wall
• Plasmodesmata -channels between adjacent
plant cells for water, nutrients…..
B. Extracellular Matrix (ECM) of Animal
Cells
• No cell walls
• Functions :
Support, Adhesion, Movement, Regulation
• Structure
– Glycoproteins: bind to receptor proteins in membrane called
integrins
• Integrins “glue cytoskeleton to ECM
Collagen
EXTRACELLULAR FLUID
Proteoglycan
complex
Fibronectin
Integrins
Plasma
membrane
Microfilaments
CYTOPLASM
Collagen in the ECM
of cartilage
Collagen, fibronectin and laminin
C. Intercellular Junctions
• Function
– Adherance, communication through direct physical contact
• 4 Types:
– Plasmodesmata- plant cells
– Tight junctions
– Desmosomes
– Gap junctions
• Tight junction seals
against fluid and
ions
• Desmosome in cells that experience
mechanical stress (skin)
• Gap junction connects cytoplasm to allow
small molecules, ions to pass from cell to cell
– connexin protein
Tight junction
0.5 µm
Tight junction
Desmosome
Gap
Desmosome
1 µm
junctions
Plasma membranes
Space
between
of adjacent cells
cells
Extracellular
Gap junction
matrix
0.1 µm
The Cell: Living Unit Greater Than Sum of Its Parts
• integration of structures and organelles to
function
• example, a macrophage’s ability to destroy
bacteria involves coordinating cytoskeleton,
lysosomes, and plasma membrane