Embed Size (px)
Citation preview
Chapter 7
• A Tour of the Cell
microscopes
• Glass lenses were invented in Middle East
• Came to Europe after crusades
• 1600- 1700’s – compound two lenses 1,000 x upper limit
1665 – Robert Hooke found dead “cells” in cork
Molecular Expressions Microscopy Primer: Museum of
Microscopy - Hooke's Microscope
1673 – Anton van Leeuwenhoek observed microscopic living organisms “animicules”
1824– Henri Dutrochet – all living things are made of cells
1831 – Robert Brown (the Brownian motion guy)– observed the nucleus
1838 - Schleiden- all plants are made of cells
1839- Schwann - animals are made of
cells
SchleidenSchwann
1850- Louis Pasteur – pasteurization (of wine)
1855- Dr. Virchow- physician- cells come from preexisting cells
1860s Civil War soldiers died from infections
The Cell Theory
1. 1. All living things are composed of one or
more cells
2. The cell is the basic unit of structure and
function
1. 3.All cells come from preexisting cells
1950’s Electron microscope (EM)-thousands of times more powerful
but not alive (TEM)
1970’s Scanning em.-(SEM) 3d images
1980’s - scanning tunneling EM- you can
see individual atoms and
push them around
So the
Japanese
pushed CO
Cell Fractionation
• Is used to separate the various parts of cells for further study.
• An example of reductionism.
• You blend the cells to break them open and spin them down to separate heavier parts.
TWO CELL TYPES
1) Prokaryote cells
• 1) Prokaryote cells (no nucleus) before nucleus
• Domains Eubacteria and Archaea
• - Bacteria Kingdom Monera
• - single celled
2) Eukaryotic cells (has nucleus)
•
• Domain Eukarya
• - membrane bound organelles
• Kingdom
– Protists Protista
• fungus Fungi
• plants Plantae
• animals Animalia
Limits to cell size
• Lower limit to cell size:
• The cell must be big enough to contain DNA, RNA and several ribosomes.
20 to 100 nanometer
Upper Limits to Cell Size: The cell must be small because:
1) Diffusion- materials (H20 and CO2) can only diffuse so far so fast
•
• 2) DNA- controls cell functions bigger cells either split or have many nuclei.
•
• Most importantly
• 3) Surface area to volume ratio
Surface Area vs. Volume Ratio
0
1
2
3
4
5
6
71 3 5 7 9
11
13
15
Size of Object
Rati
o
Cube
Sphere
Long cylinder
Squat cylinder
Surface Area to Volume Ratio
0
500
1000
1500
1 5 9 1
3
1
7
Size of Cell
Ra
tio
SA
:V X
:1 Series1
Cube
sphere
tall cylinder
squat cylinder
Parts of the Eukaryotic Cell
• Cells are compartmentalized by membranes to allow the many different reactions to occur simultaneously. Many reactions occur in the membrane lining.
• Organelles - are specialized internal structures.
Prokaryote
bacteria cellsTypes of cells
Eukaryote
animal cells
- no organelles
- organelles
Eukaryote
plant cells
Why organelles?• Specialized structures
– specialized functions
• cilia or flagella for locomotion
• Containers
– partition cell into compartments
– create different local environments
• separate pH, or concentration of materials
– distinct & incompatible functions
• lysosome & its digestive enzymes
• Membranes as sites for chemical reactions
– unique combinations of lipids & proteins
– embedded enzymes & reaction centers
• chloroplasts & mitochondria
mitochondria
chloroplast
Golgi
ER
Cells gotta work to live! • What jobs do cells have to do?
– make proteins
• proteins control everycell function
– make energy
• for daily life
• for growth
– make more cells
• growth
• repair
• renewal
Proteins do all the work!
cells
DNA
proteins
organism
Repeat after me…Proteins do all the work!
Cells functions • Building proteins
– read DNA instructions
– build proteins
– process proteins
• folding
• modifying– removing amino acids
– adding other molecules
» e.g, making glycoproteinsfor cell membrane
– address & transport proteins
Building Proteins
• Organelles involved– nucleus
– ribosomes
– endoplasmic reticulum (ER)
– Golgi apparatus
– vesicles
nucleus ribosome ERGolgi
apparatusvesicles
The Protein Assembly Line
nuclearpores
nuclearpore
nuclear envelope
nucleolus
histone protein
chromosome
DNA
• Function
– protects DNA
• Structure
– nuclear envelope
• double membrane
• membrane fused in spots to create pores– allows large macromolecules to pass through
Nucleus
What kind of molecules need to pass through?
DNA
NucleusmRNA
nuclearmembrane
smallribosomalsubunit
largeribosomalsubunit
cytoplasm
mRNA
nuclear pore
production of mRNA
from DNA in nucleus
mRNA travels from
nucleus to ribosome in
cytoplasm through
nuclear pore
1
2
Nucleolus
• Function
– ribosome production
• build ribosome subunits from rRNA & proteins
• exit through nuclear pores to cytoplasm & combine to form functional ribosomes
smallsubunit
large subunit
ribosome
rRNA &proteins
nucleolus
smallsubunit
largesubunitRibosomes
• Function
– protein production
• Structure
– rRNA & protein
– 2 subunits combine 0.08mm
Ribosomes
RoughER
SmoothER
membrane proteins
Types of Ribosomes• Free ribosomes
– suspended in cytosol
– synthesize proteins that function in cytosol
• Bound ribosomes
– attached to endoplasmic reticulum
– synthesize proteins for export or for membranes
Endoplasmic Reticulum• Function
– processes proteins
– manufactures membranes
– synthesis & hydrolysis of many compounds
• Structure
– membrane connected to nuclear envelope & extends throughout cell
Types of ER
rough smooth
Rough ER function
• Produce proteins for export out of cell– protein secreting cells
– packaged into transport vesicles for export
Which cellshave lot of rough ER?
Smooth ER function
• Membrane production
• Many metabolic processes
– synthesis
• synthesize lipids – oils, phospholipids, steroids & sex hormones
– hydrolysis
• hydrolyze glycogen into glucose– in liver
• detoxify drugs & poisons– in liver
– ex. alcohol & barbiturates
Membrane Factory
• Build new membrane– synthesize
phospholipids• builds membranes
– ER membrane expands• bud off & transfer to
other parts of cell that need membranes
Synthesizing proteins
cytoplasm
cisternalspace
mRNA
ribosome
membrane ofendoplasmic reticulum
polypeptide
signalsequence
ribosome
Golgi Apparatus
Which cellshave lots of Golgi?
transport vesicles
secretoryvesicles
• Function
– finishes, sorts, tags & ships cell products
• like “UPS shipping department”
– ships products in vesicles
• membrane sacs
• “UPS trucks”
Golgi Apparatus
Vesicle transport
vesiclebuddingfrom roughER
fusionof vesiclewith Golgiapparatus
migratingtransportvesicle
protein
ribosome
DNA
RNA
ribosomes
endoplasmic
reticulum
vesicle
Golgi
apparatus
vesicle
proteinon its way!
protein finishedprotein
Making Proteins
TO:
TO:
TO:
TO:
nucleus
proteins
transportvesicle
Golgiapparatus
vesicle
smooth ER
rough ER
nuclear pore
nucleus
ribosome
cellmembrane protein secreted
cytoplasm
Making proteinsPutting it together…
Lysosomes
small food
particle
vacuole
digesting food
lysosomes
• Function
– digest food
– clean up & recycle• digest broken
organelles
• Structure
– membrane sac of digestive enzymes
digesting brokenorganelles
When things go bad…
• Diseases of lysosomes are often fatal– digestive enzyme not working in lysosome
– picks up biomolecules, but can’t digest one
• lysosomes fill up with undigested material
– grow larger & larger until disrupts cell & organ function
• lysosomal storage diseases– more than 40 known diseases
• example:Tay-Sachs diseasebuild up undigested fat in brain cells
Phagocytosis macrophages white blood cells
• Autophagy – recycling your own stuff
• Lysosomes absorb and digest stuff in cells.
• Liver cells recycle ½ of all macromolecules everyday.
But sometimes 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” process
– lysosomes 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
15 weeks
6 weeks
syndactyly
Making Energy
• Cells must convert incoming energy to forms that they can use for work
– mitochondria:from glucose to ATP
– chloroplasts:from sunlight to ATP & carbohydrates
• ATP = active energy
• carbohydrates = stored energy
+
ATP
ATP
Mitochondria & Chloroplasts
• Important to see the similarities
– transform energy
• generate ATP
– double membranes = 2 membranes
– semi-autonomous organelles
• move, change shape, divide
– internal ribosomes, DNA & enzymes
Mitochondria
• Function
– cellular respiration
– generate ATP
• from breakdown of sugars, fats & other fuels
• in the presence of oxygen
– break down larger molecules into smaller to generate energy = catabolism
– generate energy in presence of O2 = aerobic respiration
Mitochondria• Structure
– 2 membranes• smooth outer membrane
• highly folded inner membrane
– cristae
– fluid-filled space between 2 membranes
– internal fluid-filled space• mitochondrial matrix
• DNA, ribosomes & enzymes
Why 2 membranes?
increase surface area for membrane-bound
enzymes that synthesize ATP
Mitochondria
Membrane-bound Enzymes
glucose + oxygen carbon + water + energydioxide
C6H12O6 6O2 6CO2 6H2O ATP + + +
Dividing Mitochondria
Who else divides like
that?
What does this tell us about the
evolution of eukaryotes?
Mitochondria• Almost all eukaryotic cells have mitochondria
– there may be 1 very large mitochondrion or 100s to 1000s of individual 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
Mitochondria are everywhere!!
animal cells plant cells
Chloroplasts
• Chloroplasts are plant organelles
– class 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
• Structure– 2 membranes
– stroma = internal fluid-filled space
• DNA, ribosomes & enzymes
• thylakoids = membranous sacs where ATP is made
• grana = stacks of thylakoids
Why internal sac membranes?
increase surface area for
membrane-bound enzymes that
synthesize ATP
Membrane-bound Enzymes
+ water + energy glucose + oxygencarbondioxide
6CO2 6H2O C6H12O6 6O2lightenergy
+ ++
Chloroplasts
• Function
– photosynthesis
– generate ATP & synthesize sugars
• transform solar energy into chemical energy
• produce sugars from CO2 & H2O
• Semi-autonomous• moving, changing shape & dividing
• can reproduce by pinching in two
Who else divides like
that?
bacteria!
Chloroplasts
Why are chloroplasts green?
Mitochondria & chloroplasts are different
• Organelles not part of endomembrane system
• Grow & reproduce
– semi-autonomous organelles
• 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
Food & water storage
plant cells
central vacuole
contractile
vacuole
food vacuoles
animal cells
Vacuoles & vesicles
• Function
– little “transfer ships”
• Food vacuoles
– phagocytosis, fuse with lysosomes
• Contractile vacuoles
– in freshwater protists, pump excess H2O out of cell
• Central vacuoles
– in many mature plant cells
Cytoskeleton
• Function
– structural support• maintains shape of cell
• provides anchorage for organelles– protein fibers
» microfilaments, intermediate filaments, microtubules
– motility• cell locomotion
• cilia, flagella, etc.
– regulation
• organizes structures & activities of cell
actin
microtubule
nuclei
Cytoskeleton
Centrioles • Cell division
– in animal cells, pair of centriolesorganize microtubules• spindle fibers
– guide chromosomes in mitosis
Cells need to make more cells!• Making more cells
– to replace, repair & grow, the cell must…• copy their DNA
• make extra organelles
• divide the new DNA & new
organelles between 2 new
“daughter” cells
– organelles that do this work…• nucleus
• centrioles
Centrioles
• Function– help coordinate cell division
• Structure– one pair in each cell
– “motor” proteins
Putting it all together
animal cells plant cells
Chapter 8
Membrane Structure and Function
Cell Membrane A. Phospholipid bilayer
AMPHIPATHIC molecule
1. polar head (hydrophillic)
2 nonpolar tails (hydrophobic)
Phospholipids will form layers and bilayers in water
Arranged as a Phospholipid bilayer
polarhydrophilicheads
nonpolarhydrophobictails
polarhydrophilicheads
• Serves as a cellular barrier / border
H2Osugar
lipids
salt
waste
impermeable to polar molecules
Freeze fracturing
revealed the structure
Types of movement
Studies with mouse cells showed that the lipids can move, think
ping pong balls on a pool.
Trans-membrane
protein
Membranes have
sidedness (inside versus
outside)
Overview• Cell membrane separates living cell from nonliving
surroundings
– thin barrier = 8nm thick
• Controls traffic in & out of the cell
– selectively permeable
– allows some substances to cross more easily than others• hydrophobic vs hydrophilic
• Made of phospholipids, proteins & other macromolecules
Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembraneproteins
Filaments ofcytoskeleton
Peripheralprotein
Glycoprotein
Phospholipids
Membrane fat composition varies• Fat composition affects flexibility
– membrane must be fluid & flexible
• about as fluid as thick salad oil
– % unsaturated fatty acids in phospholipids
• keep membrane less viscous
• cold-adapted organisms, like winter wheat – increase % in autumn
– cholesterol in membrane
Membrane Proteins• Proteins determine membrane’s specific functions
– cell membrane & organelle membranes each have unique
collections of proteins
• Membrane proteins:
– peripheral proteins
• loosely bound to surface of membrane
• cell surface identity marker (antigens)
– integral proteins• penetrate lipid bilayer, usually across whole membrane
• transmembrane protein
• transport proteins
– channels, permeases (pumps)
2007-2008
Why areproteins the perfect molecule to build structures in the cell membrane?
Classes of amino acidsWhat do these amino acids have in common?
nonpolar & hydrophobic
Classes of amino acidsWhat do these amino acids have in common?
polar & hydrophilic
I like thepolar onesthe best!
Proteins domains anchor molecule• Within membrane
– nonpolar amino acids • hydrophobic
• anchors protein into membrane
• On outer surfaces of membrane
– polar amino acids
• hydrophilic
• extend into extracellular fluid & into cytosol
Polar areasof protein
Nonpolar areas of protein
NH2
H+
COOH
Cytoplasm
Retinalchromophore
Nonpolar(hydrophobic)a-helices in thecell membrane H+
Porin monomer
b-pleated sheets
Bacterialoutermembrane
proton pump channel
in photosynthetic bacteria
water channel
in bacteria
function through
conformational change =
shape change
Examples
Many Functions of Membrane Proteins
Outside
Plasmamembrane
Inside
Transporter Cell surfacereceptor
Enzyme
activity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
Membrane carbohydrates • Play a key role in cell-cell recognition
– ability of a cell to distinguish one cell from another
• antigens
– important in organ & tissue development
– basis for rejection of foreign cells by immune system
Diffusion• 2nd Law of Thermodynamics
governs biological systems– universe tends towards disorder (entropy)
Diffusion
movement from high low concentration
Diffusion• Move from HIGH to LOW concentration
– “passive transport”
– no energy needed
diffusion osmosis
movement of water
Diffusion across cell membrane• Cell membrane is the boundary between
inside & outside…
– separates cell from its environment
INfood
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUTwaste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out
IN
OUT
Can it be an impenetrable boundary? NO!
Diffusion through phospholipid bilayer
• What molecules can get through directly?– fats & other lipids
inside cell
outside cell
lipid
salt
aa H2Osugar
NH3
What molecules can
NOT get through
directly?
polar molecules
H2O
ions
salts, ammonia
large molecules
starches, proteins
Channels through cell membrane• Membrane becomes semi-permeable with
protein channels
– specific channels allow specific material across cell membrane
inside cell
outside cell
sugaraaH2O
saltNH3
Facilitated Diffusion• Diffusion through protein channels
– channels move specific molecules across cell membrane
– no energy needed
“The Bouncer”
open channel = fast transport
facilitated = with help
high
low
2007-2008
The Special Case of Water
Movement of water across the cell membrane
Osmosis is diffusion of water
• Water is very important to life, so we talk about water separately
• Diffusion of water from high concentration of water to low concentration of water
– across a semi-permeable membrane
Concentration of water• Direction of osmosis is determined by
comparing total solute concentrations
– Hypertonic - more solute, less water
– Hypotonic - less solute, more water
– Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
freshwater balanced saltwater
Managing water balance• Cell survival depends on balancing water
uptake & loss
Managing water balance• Isotonic
– animal cell immersed in mild salt solution
• example:blood cells in blood plasma
• problem: none
– no net movement of water» flows across membrane equally, in
both directions
– volume of cell is stable
balanced
Managing water balance• Hypotonic
– a cell in fresh water
• example: Paramecium
• problem: gains water,
swells & can burst
– water continually enters
Paramecium cell
• solution: contractile vacuole
– pumps water out of cell
– ATP
– plant cells• turgid
freshwater
ATP
Water regulation
• Contractile vacuole in Paramecium
ATP
Managing water balance• Hypertonic
– a cell in salt water
• example: shellfish
• problem: lose water & die
• solution: take up water or pump out salt
– plant cells• plasmolysis = wilt
saltwater
Aquaporins• Water moves rapidly into & out of cells
– evidence that there were water channels
1991 | 2003
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
Cell (compared to beaker) hypertonic or hypotonic
Beaker (compared to cell) hypertonic or hypotonic
Which way does the water flow? in or out of cell
.05 M .03 M
Osmosis…
Active Transport
“The Doorman”
conformational change
• Cells may need to move molecules against concentration gradient– shape change transports solute from
one side of membrane to other
– protein “pump”
– “costs” energy = ATP
ATP
low
high
symportantiport
Active transport• Many models & mechanisms
ATP ATP
Getting through cell membrane• Passive Transport
– Simple diffusion• diffusion of nonpolar, hydrophobic molecules
– lipids
– high low concentration gradient
– Facilitated transport• diffusion of polar, hydrophilic molecules
• through a protein channel– high low concentration gradient
• Active transport– diffusion against concentration gradient
• low high
– uses a protein pump
– requires ATPATP
Transport summary
simplediffusion
facilitated
diffusion
active
transport
ATP
How about large molecules?• Moving large molecules into & out of cell
– through vesicles & vacuoles
– endocytosis
• phagocytosis = “cellular eating”
• pinocytosis = “cellular drinking”
– exocytosis
exocytosis
Endocytosis
phagocytosis
pinocytosis
receptor-mediated
endocytosis
fuse with
lysosome for
digestion
non-specific
process
triggered by
molecular
signal
Sodium – Potassium Pump
Cotransport
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
Peroxisomes
• Other digestive enzyme sacs
– in both animals & plants
– breakdown fatty acids to sugars
• easier to transport & use as energy source
– detoxify cell
• detoxifies alcohol & other poisons
– produce peroxide (H2O2)
• must breakdown
H2O2 H2O
