The Cell Cell Types & Cell Parts. Cell Types Prokaryotic Cells or Prokaryotes The Bacteria.
The Cell
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Transcript of The Cell
The CellAP Biology
1. All organisms are made up of cells
2. The cell is the basic unit of structure and function in all organisms
3. All cells come from pre-existing cells
The Cell Theory
Underlying the diversity of life is a striking unity
Activities of lifeMost everything you think of a whole organism needing to do, must be done at the cellular level…
reproductiongrowth & developmentenergy utilizationresponse to the environmenthomeostasis
Eukaryoteanimal cellsEukaryoteanimal cells
Eukaryoteplant cellsEukaryoteplant cells
Prokaryotebacteria cells
Prokaryotebacteria cells
Types of Cells
• 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
Organellesmitochondria
chloroplast
Golgi
ER
•What jobs do cells have to do?•building proteins•proteins control every cell function
•make energy• for daily life• for growth
•build more cells•growth• reproduction• repair
DNADNA
Why study protein production?
cellscells
proteinsproteins
organismorganism
Building Proteins• Organelles involved• nucleus• ribosomes• endoplasmic reticulum
(ER)• Golgi apparatus• vesicles
nucleus ribosome ERGolgiapparatus
vesicles
The Protein Assembly Line
DNA
RNA
ribosomes
endoplasmicreticulum
vesicle
Golgi apparatus
vesicle
proteinon its way!
protein finishedprotein
Making Proteins
TO:
TO:
TO:
TO:
nucleusTO:
proteins
transportvesicle
Golgiapparatus
vesicle
smooth ER
rough ER
nuclear porenucleus
ribosome
cellmembrane protein secreted
cytoplasm
Making proteins
Putting it together…
Cells gotta live! • What jobs do cells have to do?• make proteins• proteins control every cell function
• make energy• for daily life• for growth
• build more cells• growth• reproduction• repair
ATP
Cells need power!
•Making energy• take in food & digest it• take in oxygen (O2)•make ATP• remove waste
ATP
Lysosomes• Function • little “stomach” of the cell• digests macromolecules
• “clean up crew” of the cell• cleans up broken down organelles
• Structure• vesicles of digestive enzymes
only in animal cellsonly in animal cells
Christian de Duve
1960 | 1974
Where old organellesgo to die!
Lysosomal enzymes • Lysosomal enzymes work best at pH 5• organelle creates custom pH• how? • proteins in lysosomal membrane
pump H+ ions from the cytosol into lysosome
• why? • enzymes are very sensitive
to pH• why? • enzymes are proteins —
pH affects structure• why is this an adaptation: digestive enzymes which function at pH
different from cytosol?• digestive enzymes won’t function well if some leak into cytosol =
don’t want to digest yourself!
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 • ex: self-destruct of cancerous cell
Fetal development
15 weeks
6 weeks
syndactyly
When things go wrong…
• 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
From food to 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 = immediate 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
Lynn MargulisU of M, Amherst
Membrane-bound Enzymes
glucose + oxygen carbon + water + energydioxide
C6H12O6 6O2 6CO2 6H2O ATP+ + +
Membrane-bound Enzymes
+ water + energy glucose + oxygencarbondioxide
6CO2 6H2O C6H12O6 6O2lightenergy + ++
Mitochondria are everywhere!!animal cellsanimal cells plant cellsplant cells
Cells gotta live! • What jobs do cells have to do?• building proteins• proteins control
every cell function • make energy• for daily life• for growth
• build more cells• growth• reproduction• repair
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 centrioles
organize microtubules • guide chromosomes in mitosis
2007-2008
Cell Size
Limits to cell size• Lower limit• smallest bacteria• mycoplasmas• 0.1 to 1.0 micron (µm =
micrometer)• most bacteria• 1-10 microns
• Upper limit • eukaryotic cells • 10-100 microns
micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns
What limits cell size?
• Surface to volume ratio• as cell gets bigger
its volume increases faster than its surface area• smaller objects
have greaterratio of surface area to volume 6:1 ~1:1 6:1s:v
Limits to cell size
• Metabolic requirements set upper limit• in large cell, cannot move material in
& out of cell fast enough to support life
CHO
CHO
aa
aa
CH
CO2
NH3aa
O2
CH
What’s the solution?
What process is this?
O2
O2
aa
CHO
aa
CH
O2
aa
CHO
CH
aa
O2
CO2
NH3
NH3
CO2
CO2
NH3
How to get bigger?• Become multicellular (cell divides)
O2
CHO
CHO
aa
aa
CH
CO2
NH3aa
O2
CH
But what challenges do you have to solve now?
aa
CO2
CO2
CO2
CO2
CO2
CO2 CO2
CO2
CO2
CO2
NH3
NH3 NH3
NH3
NH3
NH3
NH3NH3
O2
aa
CH
aa
CHO
O2
Phospholipid Cholesterol
Membraneproteins
Cell membrane• Exchange structure• plasma membrane functions as selective
barrier• allows passage of O2 & nutrients IN• allows passage of products & wastes OUT
Cell Membrane
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
Phospholipids
Fatty acid
Phosphate
• Fatty acid tails• hydrophobic
• Phosphate group head • hydrophilic
• Arranged as a bilayer
Structure and function relationship
Phospholipid bilayer
polarhydrophilicheads
nonpolarhydrophobictails
polarhydrophilicheads
More than lipids…
• In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer
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)
Classes of amino acidsWhat do these amino acids have in common?What do these amino acids have in common?
nonpolar & hydrophobicnonpolar & hydrophobic
Classes of amino acidsWhat do these amino acids have in common?What do these amino acids have in common?
polar & hydrophilicpolar & hydrophilic
Protein’s 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
function through conformational change = shape change
Examples
Many Functions of Membrane Proteins
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
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
Movement across the Cell Membrane
Diffusion• 2nd Law of Thermodynamics
governs biological systems• universe tends towards disorder
(entropy)
Diffusion movement from high low concentration
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
INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O
OUTwasteammoniasaltsCO2
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 Doorman”“The Doorman”
open channel = fast transport
facilitated = with help
high
low
Active Transport
“The Bouncer”“The Bouncer”
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
video
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 ATP
ATP
Transport summary
simplediffusion
facilitateddiffusion
activetransport
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-specificprocess
triggered bymolecular signal
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 stablebalanced
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
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
saltwatervideo
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…
Gradients (ATP Synthase)
Cotransport (Symport and Antiport)
Bozeman, Cell Communication
Bozeman, Signal Transduction Pathways
Cell Signals (DNA Learning Center)