Transcript CELLS

CELLS
• All organisms are
made up of cells
• The cell is the unit of
structure and function
of all living things
• Life arises from the
interaction of all
cellular components.
You must check this web site
• www.cellsalive.com
There is correlation between the
structure of cells and their function
Ex: The shapes of muscles cells, sperm cells, red
blood cells,, nerve cells are appropriate for their
function.
Example: the flat tile like epithelial cells of the skin
fit closely together making a barrier to bacterial
entrance, water loss etc.
Another way to say this is that
“shape reflects function”
10 m
Most cells are microscopic
Length of some
nerve and
muscle cells
100 mm
(10 cm)
Chicken egg
10 mm
(1 cm)
Frog egg
1 mm
100 m
Most plant and
animal cells
10 m
Nucleus
Light microscope
Most bacteria
1 m
Mitochondrion
Mycoplasmas
(smallest bacteria)
100 nm
Viruses
Ribosome
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms
Electron microscope
– Cells vary in size and shape
Human height
1m
Unaided eye
How small are cells?
History
• Robert Hook (1665) named “cells” after observing tiny
compartments in cork .
• Anton VanLeeuwenhoek (1600’s) improved the
primitive microscopes and observed one celled
organisms, even bacteria. He documented his findings
with letters and diagrams to the Royal Society (of
Science) in London.
• Robert Brown (1600’s)discovered the nucleus
• Electron microscope was developed in the late 1930’s
and allows scientist to see up to 0.5 nanometers. About
1000 times larger than regular microscopes.
How are cells studied?
Microscopes and Biochemistry
– The light microscope (LM) magnify cells up to 1000
times
• Enables us to see the overall shape and structure of a cell
Eyepiece
Ocular
lens
Objective lens
Specimen
Condenser
lens
Light
source
Figure 4.1A
– The electron microscope
Figure 4.1C
TEM 2,800 
SEM 2,000 
• Allows greater magnification and reveals cellular
details
Figure 4.1D
The cell theory (mid-1800’s)
• Mathew Schleiden and Theodor Schwann examined
plant and animal tissues and came to the conclusion
that they both consist of cells
• Rudolph Virchow came to the conclusion that young
cells come from the division of other cells
• 1. All organisms are made up of cells
• 2. Cells are the units of structure and function of all
living things, that is cells have all the properties of life.
• 3. All cells come from pre-existing cells
• Prokaryotic cells are structurally simpler than
• eukaryotic cells
– There are two kinds of cells
• Prokaryotic- No nucleus-
Colorized TEM 15,000 
Bacteria and Archeae
• Eukaryotic- have nucleus- plants, animals and fungi
Prokaryotic cell
Nucleoid
region
Nucleus
Figure 4.3A
Eukaryotic cell
Organelles
– TYPE OF CELLS: Prokaryotic and Eukaryotic
– Prokaryotic cells are small, relatively simple cells
• That do not have a membrane-bound nucleus
Prokaryotic
flagella
Ribosomes
Capsule
Cell wall
Plasma
membrane
Nucleoid region (DNA)
Pili
Eukaryotic cells have a nucleus and are
partitioned into functional compartments.
– All other forms of life( plants and animals) are
composed of complex eukaryotic cells
– Membranes form compartments inside
eukaryotic cells to facilitate metabolic activities
– A small cell has a greater ratio of surface area
to volume
• Than a large cell of the same shape
10 m
30 m
30 m
Surface area
of one large cube
 5,400 m2
10 m
Total surface area
of 27 small cubes
 16,200 m2
– A typical animal cell
• Contains a variety of membranous organelles
Smooth endoplasmic
reticulum
Nucleus
Rough
endoplasmic
reticulum
Flagellum
Not in most
plant cells
Lysosome
Ribosomes
Centriole
Peroxisome
Microtubule
Cytoskeleton
Golgi
apparatus
Plasma membrane
Intermediate
filament
Mitochondrion
Microfilament
THE CYTOSKELETON AND
RELATED STRUCTURES
The cell’s internal skeleton helps organize its
structure and activities
– A network of protein fibers
• Make up the cytoskeleton.
Tubulin subunit
Actin subunit
Fibrous subunits
7 nm
Microfilament
25 nm
10 nm
Intermediate filament
Microtubule
Functions of the cytoskeleton
– Tubules and filaments are made up of protein
fibers
– Microfilaments of actin
• Enable cells to change shape and move
– Intermediate filaments
• Reinforce the cell and anchor organelles
– Microtubules give the cell rigidity
• provide anchors for organelles and act as tracks for
organelle movement
Overview: Many cell organelles are
connected through the endomembrane
system
– All cells on earth are enclosed in membranes
that maintain internal conditions different from
the surroundings, have DNA as their genetic
material and can convert forms of energy from
one to another.
– Membranes form the boundaries of many
eukaryotic cells
• Compartmentalizing the interior of the cell and
facilitating a variety of metabolic activities
– The nucleus is the cellular control center
• Containing the cell’s DNA, which directs cellular
activities
Chromatin
Nucleolus
Nucleus
Two membranes
of nuclear
envelope
Pore
Rough
endoplasmic
reticulum
Figure 4.5
Ribosomes
ORGANELLES OF THE
ENDOMEMBRANE SYSTEM
The nucleus is the cell’s genetic control center
– The largest organelle is usually the nucleus
• Which is separated from the cytoplasm by the
nuclear envelope
Inside the nucleus
• Chromatin fibers made up of DNA
These thin fibers coil up during cell
division becoming thicker and visible. They
are called now a chromosome
Nucleolus makes ribosomes
– Ribosomes on the surface of the rough ER
• Produce proteins that are secreted,
inserted into membranes, or transported in vesicles
to other organelles
Transport vesicle
buds off
4
Ribosome
3
Secretory
(glyco-) protein
inside transport vesicle
Sugar chain
1
2
Glycoprotein
Polypeptide
Rough ER
The endomembrane system is a collection of membranous
organelles
• That manufactures and distributes cell products\
Smooth endoplasmic reticulum has a variety of functions
– Smooth endoplasmic reticulum, or smooth ER
• Synthesizes lipids
• Processes toxins and drugs in liver cells
• Stores and releases calcium ions in muscle cells
Smooth ER
Rough ER
Nuclear
envelope
Ribosomes
Rough ER
TEM 45,000
Smooth ER
– A typical animal cell
• Contains a variety of membranous organelles
Smooth endoplasmic
reticulum
Nucleus
Rough
endoplasmic
reticulum
Flagellum
Not in most
plant cells
Lysosome
Ribosomes
Centriole
Peroxisome
Microtubule
Cytoskeleton
Golgi
apparatus
Plasma membrane
Intermediate
filament
Mitochondrion
Microfilament
The Golgi apparatus finishes, sorts, and ships
cell products
– Stacks of membranous sacs receive and modify ER
products
• Then ship them to other organelles or the cell surface
“Receiving” side of
Golgi apparatus
Golgi apparatus
Golgi
apparatus
New vesicle
forming
“Shipping” side
of Golgi apparatus
Figure 4.9
Transport
vesicle from
the Golgi
TEM 130,000
Transport
vesicle
from ER
The endomembrane system
– The various organelles of the endomembrane system
• Are interconnected structurally and functionally
Rough ER
Transport vesicle
from ER to Golgi
Transport vesicle from
Golgi to plasma membrane
Plasma
membrane
Nucleus
Vacuole
Lysosome
Smooth ER
Nuclear envelope
Golgi apparatus
Mitochondria gets chemical energy from food
– Mitochondria carry out cellular respiration
It uses the chemical energy in food to make ATP for
cellular work
Mitochondrion
Outer
membrane
Inner
membrane
Cristae
Matrix
TEM 44,880
Intermembrane
space
Lysosomes are digestive compartments
within a cell
– Lysosomes are sacs of enzymes that function in
digestion within a cell
1
Rough ER
Transport vesicle
(containing inactive
hydrolytic enzymes)
Golgi
apparatus
Plasma
membrane
Engulfment
of particle
Lysosome
engulfing
damaged
organelle
2
“Food”
Lysosomes
3
5
Food
vacuole
4
Digestion
– Lysosomes in white blood cells
• Destroy bacteria that have been ingested
• lysosomes also help to digest worn out , damaged
cell parts, recycle materials within the cell and fuse
with food vacuoles to digest nutrients.
Lysosome
Figure 4.10B
TEM 8,500
Nucleus
Lysosomes in white blood cells destroy bacteria
and lysosomes also can digest other parts of the
cell
Abnormal lysosomes can cause fatal diseases
– Lysosomal storage diseases. These are rare.
• Interfere with various cellular functions
• Ex: Tay- Sachs, does not break down lipids in
nerve cell membranes. Lipids accumulate
• Pompe’s disease, lysosomes cannot digest glycogen
and it accumulates in muscle and liver cells
Peroxisomes
• Specialized vesicles that contains enzymes
(catalase) that digest hydrogen peroxide
H2 O2
• Our cells produce hydrogen peroxide during metabolism
and the enzymes in peroxisomes break it down into water
and oxygen gas which are harmless to the cell.
Plant Cells
• Three organelles animals do not have
Chloroplasts
Cell wall
Central vacuole
– A typical plant cell has some structures that an
animal cell lacks
• Such as chloroplasts and a rigid cell wall
Nucleus
Rough
endoplasmic
reticulum
Ribosomes
Smooth
endoplasmic
reticulum
Golgi
apparatus
Not in
animal
cells
Microtubule
Central
vacuole
Intermediate
filament
Chloroplast
Microfilament
Cell wall
Mitochondrion
Peroxisome
Plasma membrane
Cytoskeleton
ENERGY-CONVERTING
ORGANELLES
Chloroplasts convert solar energy to chemical
energy. This is where PHOTOSYNTHESIS
takes place
– Chloroplasts, found in plants and some protists
Convert solar energy to chemical energy in sugars
Chloroplast
Inner and outer
membranes
Granum
Intermembrane
space
TEM 9,750
Stroma
Vacuoles function in the general maintenance
of the cell
– Plant cells contain a large central vacuole,
• Which has lysosomal and storage functions
Nucleus
Chloroplast
Colorized TEM 8,700
Central
vacuole
Central vacuoles in plants
Also help increase the size of cells by
absorbing water
Are mostly water, minerals and nutrients
• Store color pigments (that attract insects)
• Store waste products and poisons
– Some protists have contractile vacuoles
• That pump out excess water
Contractile
vacuoles
LM 650
Nucleus
Organelles
•
NAME
LOCATION
• Cytoskeleton
cytoplasm
• Cytosol
cytoplasm
FUNCTION
Maintains cell shape
facilitates movement and move
materials within the cell
Protein rich fluid in which
organelles and cytoskeleton
are immersed
• Nucleus
Inside nuclear envelope
Site of most of cell’s DNA
and nucleolus
• Nucleolus
Inside the nucleus
Synthesis of ribosomal RNA
ORGANELLES
NAME
LOCATION
FUNCTION
• Rough Endoplasmic Reticulum
cytoplasm
Protein synthesis,Cell metabolism,
• Smooth Endoplasmic Reticulum
cytoplasm
Lipid synthesis, storage of calcium,
Detoxification of toxic substances
• Ribosomes
Rough ER and
free in the cytoplasm
Protein synthesis
• Vesicles
move through cytoplasm
Transport
• Golgi Bodies
cytoplasm
Processing, sorting,
shipping of proteins and lipids
• Mitochondria
cytoplasm
Gets energy from food (makes ATP
during aerobic respiration)
ORGANELLES
NAME
• Lysosomes
LOCATION
FUNCTION
cytoplasm
Digestion and breaking down of materials
(only in animal cells)
• Peroxisomes
( including the cell’s own)
cytoplasm
Sacs of enzymes that break down substances
(alcohol, amino acids) into hydrogen peroxide
and then the hydrogen peroxide into water
and oxygen.
• Plasma Membrane
all around the cell
Controls substances and signals that go in
and out of cells. Maintains shape and
volume
• Cell wall ( plant cells)
cytoplasm
Keeps water inside and limits water
uptake, protects from outside influences,
maintains shape.
ORGANELLES
NAME
LOCATION
FUNCTION
• Central vacuoles
center of plant cell
water maintenance, stores waste
cytoplasm
plastids provide nutrients and
(plant cells only)
• Plastids
(plant cells only)
• Chloroplast
(plant cells only)
pigmentation
many throughout
carry out photosynthesis
the cytoplasm
contain chlorophyll
CELL JUNCTIONS
• What are junctions? Protein or cytoplasmic
bridges that serve as physical links between
cells.
• The junctions between cells help integrate cells
into tissues and higher levels of functioning.
Junctions make cells living units greater than
each individual part.
• Junctions serve to send and receive signals and
materials and to cement itself to other cells and
junctions coordinate cell activities.
Plant cells
Plants are covered by cell walls composed of
cellulose fibers.
Cell walls have plasmodesmata, these are
channels that pass through adjoining cell
walls connecting plant cell to plant cell.
Animal cells:
Junctions
• There are different kinds of intracellular
junctions between animal cells, integrating each
cell into a greater unit.
• Tight junctions
• Desmosomes or Anchoring juctions:
• Gap or Communication junctions:
Tight junctions
They fuse cell to cell to prevent leakage. Ex:
cells of the lining of the intestines keeping
the fluid inside. All cells of most tissues are
joined this way. The skin and the lining of
internal cavities (epithelial).
Gap or Communication junctions:
Link the cytoplasm of neighboring cells. They are
open channels that allow a flow of materials
and signals between cells.
• Very common in embryos and in heart tissue to
allow for the passage of ions to cause
contraction
Desmosomes or Anchoring juctions:
Joins cells in tissues of the skin, heart and
other organs such as the bladder subject to
stretching.
– Tight junctions can bind cells together into
leakproof sheets
– Anchoring junctions link animal cells into strong
tissues
– Gap junctions allow substances to flow from cell to
cell
Tight junctions
Anchoring junction
Gap junctions
Extracellular matrix
Space between cells
Figure 4.18B
Plasma membranes of adjacent cells
Cilia and flagella
• move when microtubules bend
Figure 4.17A
LM 600
Colorized SEM 4,100
– Eukaryotic cilia and flagella are locomotor
appendages that protrude from some cells
Figure 4.17B
Clusters of microtubules
Drive the whipping action of these organelles
.
Flagellum
Electron micrographs
of cross sections:
Outer microtubule
doublet
TEM 206,500
Central
microtubules
Radial spoke
Dynein arms
Flagellum
TEM 206,500
Plasma
membrane
Basal body
(structurally identical to
centriole)
Basal body
PLASMA MEMBRANE
• Function:
The cell’s “gate keeper”. Very important.
It controls what goes in and out of a cell.
Keeps equilibrium between the inside of cells
and the outside and promotes homeostasis.
Web site to check:
http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101
Membranes
• http://www.wiley.com/legacy/college/boyer/
0470003790/animations/membrane_transpo
rt/membrane_transport.htm
The plasma membrane of the cell is
selectively permeable
Controlling the flow of substances into or
out of the cell
TEM 200,000 
Outside
of cell
Cytoplasm
PLASMA MEMBRANE
STRUCTURE:
It is a LIPID BILAYER. Its main component is a
PHOSPHOLIPID molecule.
• A phospholipid is made up of a hydrophilic head (water loving)
and two hydrophobic fatty acid tails (dislike water). These are
arranged in two layers with the fatty acids tails sandwiched
between the hydrophilic heads.
• The membrane is “fluid”, it moves about, tails twist and wave
• Embedded in the phospholipid bilayer are the surface proteins.
• The membrane is “a mosaic” of different proteins embedded in
the fluid matrix of the lipid bilayer.
What makes up the plasma membrane?
– Phospholipids are the main structural
components of membranes
Membrane phospholipids form a bilayer
• Have a hydrophilic head
and two hydrophobic tails
Hydrophilic head
Phosphate
group
CH2
O
C O
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
O
+ CH3
CH2 N CH3
CH3
CH2
O
P O–
O
CH2
CH
O
C O
CH2
CH2
CH2
CH2
CH2
CH2
Symbol
CH2
CH
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
Hydrophobic tails
Phospholipids form a two-layer sheet
Called a phospholipid bilayer, with the heads
facing outward and the tails facing inward
Water
Hydrophilic
heads
Hydrophobic
tails
Water
How does it work?
• Membrane is selectively permeable or semipermeable. Small molecules that are
electrically neutral diffuse easily in and out
such as O2, CO2, and alcohols.
• The non-polar phospholipid tails of the bilayer
repel charged molecules but allow lipid soluble
molecules to pass easily.
• Sugars need to be transported through a
channel as well as charged ions such as H+,
Na+, K+, Cl
• Large molecules (like proteins) cannot diffuse through
and must enter the cell by other mechanisms such as active
transport. Active transport uses energy (ATP) to “push” the
molecules in and out.
• Serious diseases associated with cell membrane defects:
Multiple Sclerosis, there is a myelin cover on axons of nerve
cells. Because it is defective muscle control is lost
Cystic Fibrosis, The channels for chloride to pass through the
membrane do not work. Chloride ion are not able to leave
the cell. Results in thick mucus in respiratory track and
other ducts in the body.
Proteins found in the plasma membrane:
• Integral penetrate the hydrophobic core of the
lipid bilayer
• Peripheral are loosely bound to the surface of
the membrane
•
•
•
•
Transport proteins
Receptor proteins
Recognition proteins
Adhesion proteins
Proteins found in the plasma membrane:
• Transport proteins:
These are open on both sides making a channel, a passage. Water soluble
substances pass through it. It is very specific for the substance that it moves.
• Receptor proteins:
Grab or bind substances to pass them through. Have a binding site with a
specific shape that fits the shape of another molecule. It can bind a chemical
messenger such as a hormone which then causes a change in the shape of the
protein that relays the message to the inside of the cell.
• Recognition proteins:
These are glycoproteins. Have a short chain of sugars attached to it.
Are like fingerprints. Serve as identification tags that are recognized by other
cells. Your cells recognize “your own”
• Adhesion proteins:
Like “glue”, make cells stick together.
The membrane is a fluid mosaic of phospholipids
with proteins and other molecules embedded in a
phospholipid bilayer
Fibers of the
extracellular
matrix
Carbohydrate
(of glycoprotein)
Glycoprotein
Glycolipid
Plasma
membrane
Phospholipid
Proteins
Microfilaments
of cytoskeleton
Cholesterol
Cytoplasm
Membrane proteins also function in transport
Moving substances across the membrane
ATP
Other membrane proteins
Function as receptors for chemical
messages from other cells
Messenger molecule
Receptor
Activated
molecule
Many membrane proteins
Function as enzymes