Transcript A Tour of the Cell

The Cell
Cell Theory
 Cells
are the fundamental units of life.
 All
living organisms are composed of cells.
 All
cells come from preexisting cells.
 The
cell is the simplest collection of matter that can live.
 Even
when arranged into higher levels of organizations,
such as tissues and organs, cells are an organism’s basic
structure and function.
Cell

Life at the cellular level arise from structural order, reflecting
emergent properties and the correlation between structure and
function.
 The
movement of an animal cell depends on the intricate interplay of the
structures that make up a cellular skeleton.
 Organisms
interact with their environment; cells sense and respond to
environmental fluctuations.

Evolution is the unifying biological theme.

All cells are related by their descent from earlier cells but have been modified in
various ways during the history of life.
Why are cells so small?
Why can’t they be as huge as an hippo?
What limits cell size?
 Surface
to volume ratio
 as
cell gets bigger its volume increases faster
than its surface area
 smaller
objects have greater
ratio of surface area to volume
What cell organelle governs this?
Why is a huge singlecelled creature not
possible?
s:v
6:1
~1:1
6:1
20052006
Limits to Cell size
 Metabolic
requirements set upper limit
 in
large cell, cannot move material in & out
of cell fast enough to support life
aa
CH
NH3
aa
CHO
O2
CH
aa
CO2
CHO
CO2
NH3
O2
NH3
CH
aa
aa
O2
CO2
CHO
O2
NH3
CHO
O2
CO2
aa
CH
aa
2005What’s the solution?
2006
How to get bigger?
Become
multi-cellular (cell divides)
CO2
CO2
aa
O2
CH
aa
NH3
CO2
CO2
CO2
CHO
NH3
CHO
CH
O2
aa
aa
O2
aa
NH3
CO2
CO2
CO2
NH3
NH3
CO2
CH
NH3
NH3
CO2
NH3
O2
NH3
CHO
CO2
aa
20052006
Cell characteristics
 All
cells:
 surrounded
 have
cytosol
 semi-fluid
substance within the membrane
 cytoplasm
 contain
 have
 tiny
by a plasma membrane
= cytosol + organelles
chromosomes which have genes in the form of DNA
ribosomes
“organelles” that make proteins using instructions contained in genes
Types of cells
Prokaryote
bacteria cells
- no organelles
- organelles
Eukaryote
animal cells
Eukaryote
plant cells
Types of cells
 Prokaryotic vs. eukaryotic cells
Prokaryotic cell
Eukaryotic cell

DNA in nucleoid region,
without a membrane
separating it from rest of cell

chromosomes in nucleus,
membrane-enclosed
organelle

Cell wall present in all (type
differs)

Cell walls present in fungi and
plants only

More complex

Membrane bound organelles
present
The prokaryotic cell is much simpler in structure, lacking a nucleus
2005-2006
and the other membrane-enclosed organelles of the eukaryotic cell.
Why organelles?

Specialized structures

specialized functions


cilia or flagella for locomotion
Containers

partition cell into compartments

create different local environments


chloroplast
separate pH, or concentration of materials
distinct & incompatible functions


mitochondria
lysosome & its digestive enzymes
Membranes as sites for chemical reactions

unique combinations of lipids & proteins

embedded enzymes & reaction centers

chloroplasts & mitochondria
Golgi
ER
Cells gotta work to live!
 What
jobs do cells have to do?
make
proteins
 proteins
make
control every cell function
energy
 for
daily life
 for
growth
make
more cells
 growth
 repair
 renewal
Nucleus
 Contains
most of the genes in a eukaryotic cell.
 Organized
Made
into discrete units called chromosomes.
up of material called chromatin.
Complex
 Nuclear
of proteins and DNA
Matrix
 Framework
interior.
of fibers that extends through the nuclear
Nucleus
 Separated
 Double
from the cytoplasm by nuclear membrane.
membrane
 Perforated
 Pore
by pores
Complex
 Protein
structure that line each pore, regulating the passage of certain large
macromolecules and particles,
 Lined
A
by nuclear lamina
network of protein filaments that maintain the shape of the nucleus.
Building Proteins
 Organelles
involved
 nucleus
 ribosomes
 endoplasmic
reticulum
(ER)
 Golgi apparatus
 vesicles
The Protein Assembly Line
nucleus
ribosome
ER
Golgi
apparatus
vesicles
Endomembrane System
Regulates protein traffic and performs
metabolic functions in the cell.
Membranes are either directly continuous
or connected via the transfer of vesicles.
Includes:
Nuclear membrane, ER, Golgi Apparatus,
lysosomes, vacuoles, and plasma
membrane
Synthesizing proteins
cisternal
space
polypeptide
signal
sequence
ribosome
ribosome
mRNA
membrane of
endoplasmic reticulum
cytoplasm
Nucleolus
 Function
ribosome
build
production
ribosome subunits from rRNA & proteins
exit
through nuclear pores to cytoplasm &
combine to form functional ribosomes
large subunit
small
subunit
rRNA &
proteins
ribosome
nucleolus
Types of Ribosomes
 Free
ribosomes
suspended
synthesize
in cytosol
 Bound
in cytosol
proteins that function
ribosomes
attached
reticulum
to endoplasmic
synthesize
proteins for export
or for membranes
membrane proteins
Rough ER function
 Finalize
protein formation and prepare for
export out of cell (protein folding)
protein secreting cells will have lots
packaged into transport vesicles to Golgi
Golgi Apparatus
Function
finishes,
like
ships
sorts, tags & ships cell products
“FedEx shipping department”
products in vesicles
membrane
“FedEx
secretory
vesicles
sacs
trucks”
transport vesicles
Putting it together…
Making proteins
nucleus
nuclear pore
cell
membrane
protein secreted
rough ER
ribosome
vesicle
proteins
smooth ER
transport
vesicle
cytoplasm
Golgi
apparatus
Smooth ER function
 Membrane
production
 Many metabolic processes
 synthesis
 synthesize
 oils,
lipids
phospholipids, steroids & sex hormones
 hydrolysis
 hydrolyze
 in
liver
 detoxify
 in
glycogen into glucose
drugs & poisons
liver
 ex.
alcohol & barbiturates
Lysosomes
only in
animal cells
Function
little
“stomach” of the cell
digests
“clean
macromolecules
up crew” of the cell
cleans
up broken down
organelles
 Structure
vesicles
of digestive enzymes
synthesized by rER,
transferred to Golgi
Cellular digestion
Lysosomes
vacuoles
fuse with food
polymers
digested into
monomers
pass
to cytosol to become
nutrients of cell
 lyso– = breaking things apart
 –some = body
vacuole
When cells need to die…
 Lysosomes
can be used to kill cells when they
are supposed to be destroyed
some
cells have to die for proper development in an
organism
apoptosis
 “auto-destruct”
 lysosomes
process
break open & kill cell
 ex:
tadpole tail gets re-absorbed
when it turns into a frog
 ex:
loss of webbing between your fingers during fetal development
Fetal development
syndactyly
6 weeks
15 weeks
Food & water storage
food vacuoles
plant cells
central vacuole
animal cells
contractile
vacuole
Vacuoles & vesicles
 Function
 little
“transfer ships”
Food
vacuoles
 phagocytosis,
Contractile
fuse with lysosomes
vacuoles
 in
freshwater protists, pump excess H2O
out of cell
Central
 in
vacuoles
many mature plant cells
Vacuoles in plants
 Functions
 storage
 stockpiling
proteins or inorganic ions
 depositing
metabolic byproducts
 storing
pigments
 storing
defensive
compounds against
herbivores
 selective
membrane
control
what comes
in or goes out.
Making Energy
 Cells
must convert incoming energy to
forms that they can use for work
mitochondria:
ATP
from glucose to ATP
chloroplasts:
from sunlight to ATP & carbohydrates
 ATP
= active energy
 carbohydrates
= stored energy
ATP
+
Mitochondria & Chloroplasts
 Important
 transform
energy
 generate
 double
to see the similarities
ATP
membranes = 2 membranes
 semi-autonomous
 move,
 internal
organelles
change shape, divide
ribosomes, DNA & enzymes
Mitochondria
Function
 cellular
respiration
 generate
ATP
 from
breakdown of sugars, fats
& other fuels - catabolism
 generate
energy in presence of O2 =
aerobic respiration
Semi-autonomous
replicate itself
– can
Mitochondria
 Almost
all eukaryotic cells have
mitochondria
number
of mitochondria is
correlated with aerobic metabolic
activity
more
activity = more energy
needed = more mitochondria
What cells would
have a lot of
mitochondria?
active cells:
• muscle cells
• nerve cells
Chloroplasts
 Chloroplasts
 class
are plant organelles
of plant structures = plastids
 amyloplasts
 store
starch in roots & tubers
 chromoplasts
 store
pigments for fruits & flowers
 chloroplasts
 store
chlorophyll & function
in photosynthesis
 in
leaves, other green
structures of plants &
in eukaryotic algae
Chloroplasts
 Function
 photosynthesis
 generate
ATP & synthesize sugars
 transform
 produce
solar energy into chemical energy
sugars from CO2 & H2O
 Semi-autonomous
 moving,
 can
changing shape & dividing
reproduce by pinching in two
Who else divides
like that?
bacteria!
Mitochondria & chloroplasts are different
from other organelles…how?

Not part of endomembrane system

Grow & reproduce

Proteins primarily from free ribosomes in cytosol & a
few from their own ribosomes

Own circular chromosome
 directs
synthesis of proteins produced by own internal
ribosomes
 ribosomes
like bacterial ribosomes
Who else has a circular chromosome not
bound within a nucleus?
bacteria
Endosymbiosis theory
 Mitochondria
& chloroplasts were once free
living bacteria
 engulfed
by ancestral eukaryote
 Endosymbiont
cell
that lives within another cell (host)
mutualistic
relationship
evolutionary advantage
for both
 one
supplies energy
 the other supplies raw materials
& protection
Lynn Margulis
U of M, Amherst
1981
Endosymbiosis theory
Evolution of eukaryotes
Cytoskeleton
 Provides
support, motility, and regulation
 Mechanical
support for shape
 Anchorage for many organelles and cytosolic enzymes
 Cytoskeleton is dynamic
Can
be dismantled and reassembled in a different part
of the cell
 Play
a role in cell location and limited movements of
parts of the cell.
Cytoskeleton

Vesicles can travel along “monorails” provided by
cytoskeleton.

Manipulates the plasma membrane to form food vacuoles
during phagocytosis.

Plays a role in the regulation of biochemical activities.
 Transmit
forces exerted by extracellular molecules
 Transmission
of naturally occurring mechanical signals may help
regulate and coordinate the cell’s response.
Classes of Cytoskeleton
 Microtubules
 Thickest, constructed of the globular protein
tubulin
 Shape and support the cell and serve as tracks
to guide motor proteins carrying organelles to
their destination.
 Responsible for the separation of chromosomes
during cell division.
 In animal cells, they grow out from a
centrosome.
 Specialized arrangement of microtubules is
responsible for the beating of cilia and flagella.
Classes of Cytoskeleton
 Microfilaments
 Solid
rods, made from molecules of actin, a globular
protein.
 Twisted double chain of actin subunits
 Present
in ALL eukaryotic cells
 Can form structural networks
 Role
is to bear tension, resisting pulling forces within the cell.
 Cortical
microfilaments form a 3D network just in side the plasma
membrane to help support the cells shape.
 Important in cell motility
Classes of Cytoskeleton

Intermediate Filaments

Built from the family of proteins that include keratins.

Specialized for bearing tension

More permanent structures than the other two.

Even after cells die the intermediate filament networks often
persist.

Reinforces cell shape and fix organelle location

Nucleus is fixed in location by branches of the filaments that extend into the cytoplasm.

Make up the nuclear lamina

Strengthens the axon of nerve cells

Function as framework of the entire cytoskeleton
Cell Wall

Found in plants, prokaryotes, fungi, and protists

Protects the cell

Maintains cell shape

Prevents excessive uptake of water

Supports the plant against the force of gravity.

Basic Design
 Microfibrils
synthase.
of cellulose synthesized by an enzyme called cellulose
Cell Wall

Primary Cell Wall


Middle Lamella


Thin layer between the primary walls with sticky polysaccharides
called pectins that glues cell together.
Secondary Cell Wall


Thin, flexible wall in young plants.
When a plant stops growing it strengthens its cell wall by secreting
hardening substances into the primary wall

Strong durable matrix that supports and protects.

Wood consists mainly of secondary walls
Plasmodesmata

Perforated channels between adjacent cells
Extracellular Matrix (ECM)


In animal cells lacking a cell wall.
Glycoproteins, especially collagen fibers,
embedded in a network of glycoprotein
proteoglycans



Proteoglycan molecules consist of a small core
protein with many carbohydrate chains covalently
attached.
In many cells, fibronectins connect to
integrins, cell-surface receptor proteins that
span the membrane and bind on their
cytoplasmic side to proteins attached o
microfilaments of the cytoskeleton.
ECM regulates cell Behavior.
Intercellular Junctions

Neighboring cells in tissues, organs, and organ systems often adhere,
interact, and communicate through direct physical contact.
 Plasmodesmata

In plant cells, allows cytosol to pass between cells.

Water and small solutes pass freely. In some cases proteins and RNA may pass.
 Animal
cells have 3 types
 Tight
Junctions  membranes of adjacent cells are fused, forming continuous
belts around cells that prevent leakage of extracellular fluids.
 Desmosomes
 Gap
Fasten cells together in strong sheets
Junctions provide cytoplasmic channels between adjacent cell

Special membrane proteins surround these pores

Ions, sugars, amino acids, and other small molecules can pass

In embryos, gap junctions facilitate chemical communication during development.