A Tour of the Cell
Lecture 2, Part 1
Fall 2008
Cell Theory
Cells are the basic unit of structure and
function
• The lowest level of structure that can
perform all activities required for life
– Reproduction
– Metabolic activity
• Cell Theory:
– All organisms are made of cells
– All cells arise from other cells
1
2
How do we
study cells?
Fig. 6.2
3
How do we study cells?
Fig. 6.4
Fig. 6.5
Cell Fractionation
4
Size & Function
• Limits to size
• Surface area to
volume ratio
Fig. 6.8
Prokaryotes & Eukaryotes
Prokaryotes
Eukaryotes
5
Prokaryotes vs. Eukaryotes
Prokaryote
What
differences do
you see?
Eukaryote
Fig. 6.6
6
7
Characteristics of all cells
•
•
•
•
Plasma membrane
Cytosol
Chromosomes
Ribosomes
Fig. 6.7
Plasma Membrane
Present in all cell types
Function:
• Separates the internal from the external
environment
• Regulate chemical exchanges within the
environment
– Chemical reactions more efficient
• Dynamic selective barrier
8
Major differences
Prokaryotes
• No nucleus
– Nucleoid region
9
Eukaryotes
• Nucleus
– (DNA in a membrane-bound
region)
• Simple
• No membrane bound
organelles
• Complex
• Membrane bound
organelles
• Smaller (1-5 nm)
• Evolutionarily older
• Larger (10-100 nm)
• Evolutionarily younger
– Organelle – a structure with a
specified function w/i a cell
Views of Prokaryote Cells
See Fig. 27.2
10
The Origin of Eukaryotic Cells
Evolution of the
endomembrane
system
• All the membrane bound
organelles within a cell,
except for mitochondria
and chloroplasts
• Inward folding of plasma
membrane formed
nuclear envelope,
organelles
11
Eukaryotes: Animal & Plant Cells
Animal cell structures:
• Plasma membrane
• Nucleus
• Cytosol
• Ribosomes
• Endoplasmic reticulum
• Golgi apparatus
• Mitochondria
• Cytoskeleton
• Vacuoles
• Peroxisome
Not typically found in plants:
• Centrosome
• Lysosomes
• Flagella
See Fig. 6.9 –Animal cell
12
Views of Animal Cells
13
Intestinal (smooth) muscle cells
Cheek cells (400X)
Cardiac muscle cells
Brain cells (astrocytes)
Eukaryotes: Animal & Plant Cells
Plant cell structures:
• Plasma membrane
• Nucleus
• Cytosol
• Ribosomes
• Endoplasmic reticulum
• Golgi apparatus
• Mitochondria
• Cytoskeleton
• Peroxisome
Not found in animals:
• Cell Wall w/plasmodesmata
• Plastids (Chloroplasts,
Amyloplasts, Chromoplasts)
• Central vacuole
Fig. 4.6 –Animal cell
See Fig. 6.9 – Plant cell
14
Views of Plant Cells
Leaf cells
15
Root cell w/amyloplasts
Plant cell
Leaf cells w/chloroplasts
Leaf epidermal (surface) cells
Cytosol
Cytoplasm
• Area between the
nucleus and the
plasma membrane
Cytosol
• Fluid of the
cytoplasm
16
Nucleus
Functions
• Store genes on chromosomes
• Regulate gene expression
• Transport regulatory factors and gene
products
• Produce messages (mRNA) that code
for proteins
• Produce the components of ribosomes
• Replication of genetic material
17
18
Nucleus
Nuclear envelope
• Double
membrane
Pore complexes
• Gatekeepers
Nuclear lamina
• Protein filaments
• Maintains shape
of nucleus
Fig. 6.10
19
Nucleus
Chromosomes
• Discrete units of DNA
• Chromatin - Association of
DNA molecules and
proteins
• One chromatin = one
chromosome
Nucleolus
• Ball-like mass of fibers &
granules
• Produces ribosomal RNA
(rRNA)
• Assembles components of
ribosomes
Fig. 6.10
Ribosomes
Complex of proteins & rRNA
Function: Protein synthesis
• Ribosome parts are made in nucleus by
nucleolus
• Parts travel out of nucleus, into cytoplasm
Two types:
• Bound ribosome
– Bound to endoplasmic reticulum (ER)
– Make proteins for membranes or exportation from cell
• Free ribosomes
– make proteins that stay
in cytosol
Fig. 6.11
20
DNA Control of the Cell
DNA – Protein
production
1. mRNA synthesis
2. mRNA travels to
ribosomes
3. Ribosomes use
mRNA to
synthesize
proteins
21
Endomembrane System
Functions:
• Manufacturing and distributing cellular products
• Detoxification of poisons
Contains:
• Nuclear envelope
• The endoplasmic reticulum (ER)
• The Golgi apparatus
• Lysosomes & Vacuoles
• Plasma membrane not Endo, but related
Membranes unique in structure & function
Membranes dynamic
22
23
Endoplasmic Reticulum
Function: manufacturing of many cellular products
• Large – more than ½ of all membrane in cell
• Continuous with nuclear envelope
• Cisternae
– Membranous tubules & sacs
– Cisternal space
Fig. 6.12
24
Endoplasmic Reticulum
Smooth ER
• No ribosomes
Functions:
• Lipid production
– E.g., steroids, phospholipds
• Metabolism of
carbohydrates
• Detoxification of drugs
• Calcium ion storage
Fig. 6.12
25
Endoplasmic Reticulum
Rough ER
• Ribosomes bound to ER
Function:
• Produces secretory
proteins
– Glycoproteins
– Transport vesicles
• Produces membrane
proteins
• Makes phospholipids for
membrane
Fig. 6.12
The Golgi Apparatus
Function:
• Receives products from ER
• Modifies products
• Stores products
• Delivers products
– Other parts of cell
– Other cells (secretion/exportation)
• Manufactures some macromolecules
Fig. 6.13
26
The Golgi Apparatus
Cis face – receiving
Trans face – shipping
• Products identified and “tagged”
e.g., phosphate groups added to
products
e.g., recognition proteins on
transport vesicles
Cisternal maturation model
• Dynamic process
• Cisturnae move from cis to trans
• Products modified as cisturnae
move
Fig. 6.13
27
28
Lysosomes
Lysosome
• Membrane bound sac of hydrolytic
enzymes
• Keeps enzymes from rest of cell
• Higher pH in lysosome optimal for
lysosomal enzymes
Production:
• ER makes hydrolytic enzymes &
lysosomal membranes
• Transported to GA for processing
• Some bud directly from GA
Fig. 6.14
29
Lysosomes
Function:
• Nutrient digestion
– Part of phagocytosis
• Destroy harmful bacteria
• Recycle damaged organelles
– Autophagy
• Embryonic development
Fig. 6.14
Vacuoles: Animal Cells
Membrane bound sacs that form (“bud”) from the
ER, Golgi apparatus or plasma membrane.
Function:
• Contain material
• Food vacuole
• Water pumps
• Contractile vacuoles
30
Central Vacuole: Plant Cells
Central Vacuole
• Large – can occupy 90% volume
of cell
• Coalescence of many smaller
vacuoles from ER, GA
• Single membrane
• Water, salts, other molecules
inside
• Few enzymes
Function
• Storage
• Growth of cell
• Protection
• Helps concentrate enzymes in
rest of cell
Fig 6.15
31
Endomembrane System
Fig. 6.16
32
33
Mitochondria
Function:
• Cellular respiration
– Converts carbon compounds into ATP
– ATP (adenosine triphosphate) –energy for cellular work
• Found in most eukaryotic cells
• Not part of endomembrane systems
• Contains its own
DNA
• Has a double
membrane
– Membrane proteins
made by free
ribosomes
• Cristae – infoldings
of inner membrane
Fig. 6.17
34
Chloroplasts
Function: Photosynthesis
• Creates carbon compounds using energy from the sun
• Contain chlorophyll a & other pigments
• Not part of endomembrane systems
• Contains its own DNA
• Has a double membrane
• Thylakoids – flattened interconnected stacks
• Granum – stacks of thylakoids
• Stroma – fluid outside thylakoids
•
•
•
Fig. 6.18
Intermembrane
space
Stroma
Thylakoid space
Other Plastids
Plastid
• Organelle with 2 membranes
• Has its own DNA & RNA
• Found in plants, some protists
Three main types
• Chloroplasts
• Chromoplasts
– Function: Stores lipid soluble pigments
– Usually colored
• Amyloplasts
– Function: Stores starch
35
Peroxisomes
• Specialized membrane compartment
• Single membrane
Function:
• Contains enzymes that transfer hydrogen to
oxygen, producing hydrogen peroxide
• Breaks down fatty acids
• Detoxify
Composed of:
• Proteins from cytosol
• Lipids from ER
• Lipids synthesized in
Peroxisome
36
Fig. 6.19