cells and how they work chapter 3. cells and how they work chapter outline cells: organized for life...
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Cells and how they work
Chapter 3
CELLS AND HOW THEY WORK
Chapter Outline
Cells: Organized for life
The cytoskeleton: support and movement
The plasma membrane: a lipid bilayer
The plasma membrane is a mix of lipids and proteins
Membrane proteins carry out most membrane functions
DNA is organized in chromosomes
Endoplasmic reticulum (ER) : A protein and lipid assembly line
Golgi Bodies: Packing and shipping Mitochondria: the cell’s energy factories
Mitochondria: the cell’s energy factories
ATP—The cell’s energy currency
How cells make ATP
Cells make ATP in three steps
Step 1: Glycolysis breaks glucose down to pyruvate
Step 2: The Krebs cycle produces energy-rich transport molecules
Step 3: Electron transport produces a large harvest of ATP
• Smallest unit of life
• Can survive on its own or has potential
to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
Cell
Structure of Cells
All start out life with:– Plasma membrane
– Region where DNA is stored
– Cytoplasm
Two types:– Prokaryotic
– Eukaryotic
PLASMA MEMBRANE GOLGI BODY LYSOSOME
ENDOPLASMIC RETICULUM (ER)
nuclear envelope
nucleolusNUCLEUS MITOCHONDRION
microfilaments
microtubules
components ofcytoskeleton
plasma membrane
mitochondrion
nuclear envelope
nucleolus
DNA + nucleoplasm
NUCLEUS
vesicle
lysosome
rough ER
ribosomes
smooth ER
vesicle
Golgi body
pair ofcentrioles
Table 3.2 Common Features of Eukaryotic Cells
ORGANELLES AND THEIR MAIN FUNCTIONS:
Nucleus
Endoplasmic reticulum (ER)
Golgi body
Various vesicles
Mitochondria
Contains the cell’s DNA
Routes and modifies newly formed polypeptide chains; also, where lipids are assembled
Modifies polypeptide chains into mature proteins; sorts and ships proteins and lipids for secretion or for use inside cell
Transport or store a variety of substances; break down substances and cell structures in the cell; other functions
Produce ATP
Table 3.2 Common Features of Eukaryotic Cells
OTHER STRUCTURES AND THEIR FUNCTIONS:
Ribosomes
Cytoskeleton
Assemble polypeptide chains
Gives overall shape and internal organization to cell; moves the cell and its internal parts
Electron MicroscopeElectron Microscope
Light MicroscopeLight Microscope
• Basis for cell shape
• Enables organelle movement within cells and, in some cases, cell motility
• Main elements are microtubules, microfilaments, and filaments
Cytoskeleton
microtubules
intermediate filaments
microfilaments
Figure 3.13Figure 3.13
Flagella and Cilia
• Structures for
cell motility
• 9+2 internal
structure
• Arise from
centriolesdynein
microtubule
one of the outer ring’s pairs of microtubules(doublets)
dynein arm
two centralmicrotubules
central sheath
base of flagellum or cilium
plasma membrane
basal body
plasma membrane
• Main component of cell membranes
• Gives membrane its fluid properties
• Two layers of phospholipids– Hydrophilic heads face outward
– Hydrophobic tails in center
Lipid Bilayer
lipid bilayer
water
water
one layer of lipids
one layer of lipids
Plasma Membrane
• Extremely thin
• Mosaic of proteins and lipids
• Lipids give membrane its fluid quality
• Proteins carry out most membrane
functions
Membrane Proteins
• Transport proteins
• Receptor proteins
• Recognition proteins
• Adhesion proteins
EXTRACELLULAR FLUID
cytoskeletal proteins just beneath the plasma membrane
adhesion protein
phospholipid cholesterol
LIPID BILAYER
recognition protein
receptor protein
CYTOPLASMtransport proteins
In-text figurePage 50oxygen, carbon dioxide,
and other small, nonpolar molecules; some water
molecules
glucose and other large, polar, water-soluable molecules; ions
(e.g., H+, Na+, K+, Ca++, CI–)
Membrane Proteins
• Transport proteins
• Receptor proteins
• Recognition proteins
• Adhesion proteins
glucose, more concentrated outside cell than inside
glucosetransporter
When the glucose bindingsite is again vacant, the protein resumes its original shape.
Glucose binds to a vacant site inside the channel through the transport protein.
Glucose becomes exposed to fluid on the other side of the membrane.
Bound glucose makes the protein change shape. Part of the channel closes behind the solute.
Passive Transport
• Flow of solutes through the interior of passive transport proteins down their concentration gradients
• Passive transport proteins enable solutes to move both ways
• Does not require any energy input
Active Transport
• Net diffusion of solute is against concentration gradient
• ATP gives up phosphate to activate protein
• Binding of ATP changes protein shape and affinity for solute
higher concentration of calcium outside cell
lower concentration of calcium inside cell
The pump returns toits resting shape.
ATP binds to a calcium pump.
Shape change permits calcium release at opposite side of membrane. Phosphate group and ADP are released.
Calcium enters tunnel through pump.
ATP transfers a phosphate group to pump. This energy input will cause pump’s shape to change.
Components of Nucleus
Nuclear envelope
Nucleoplasm
Nucleolus
nuclear pore (protein complex that spans both lipid bilayers)
one of two lipid bilayers(facing cytoplasm)
one of two lipid bilayers(facing nucleoplasm)
NUCLEAR ENVELOPE
• Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm
• Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells
Functions of Nucleus
Endoplasmic Reticulum
• In animal cells, continuous with nuclear
membrane
• Extends throughout cytoplasm
• Two regions: rough and smooth
Rough ER
• Arranged into flattened sacs
• Ribosomes on surface give it a rough
appearance
• Some polypeptide chains enter and are
modified
cytoplasm ribosomevesicle
RNA messages from the nucleus
the cell nucleus rough ER
Smooth ER
• A series of interconnected tubules
• No ribosomes on surface
• Lipids assembled inside tubules
Golgi Bodies
• Put finishing touches on proteins and lipids that arrive from ER
• Package finished material for shipment to final destinations
internal space
budding vesicle
5 Vesicles from the Golgi body transport products to the plasmamembrane. Products arereleased by exocytosis.
4 Proteins and lipids take onfinal form inside Golgi body. Modifications enable them to be sorted out and shipped to proper destinations.
3 Vesicles bud from the ERmembrane and transportunfinished proteins and lipids to a Golgi body.
2 In the membrane of smoothER, lipids are assembled.
1 Some polypeptide chainsenter the rough ER. Modifications begin.
Endocytic vesicles format plasma membrane andmove into the cytoplasm. They might fuse withthe membrane of otherorganelles or remain intact, asstorage vesicles.
Exocytic vesicles budfrom ER and Golgimembranes, travel to and fuse with plasma membrane.Their contents are therebyreleased from the cell.
DNA instructions forbuilding polypeptidechains leave the nucleusand enter the cytoplasm.
assorted vesicles
Golgibody
smooth ER
rough ER
Chains are assembled on ribosomes in cytoplasm.
Vesicles
• Membranous sacs that move
through the cytoplasm
• Lysosomes
• Peroxisomes
©2005 Brooks/Cole - Thomson
plasma membrane
endocytic vesicle forming
exocytic vesicle leaving cytoplasm
Mitochondrial Structure
• Outer membrane faces cytoplasm
• Inner membrane folds back on itself
• Membranes form two distinct compartments
• ATP-making machinery is embedded in the inner mitochondrial membrane
• ATP-producing powerhouses
• Double-membrane system
• Carry out the most efficient
energy-releasing reactions
• Reactions require oxygen
Mitochondria
cristae
inner membraneouter mitochondrial membrane
outer compartment
inner compartment
inner compartment outer compartment cytoplasm
outer mitochondrial membrane
inner mitochondrial membrane
• Glucose is absorbed into blood
• Pancreas releases insulin
• Insulin stimulates glucose uptake by cells
• Cells convert glucose to glucose-6-phosphate
• This traps glucose in cytoplasm where it can
be used for glycolysis
Carbohydrate Breakdown and Storage
Glycolysis
• Occurs in cytoplasm
• Reactions are catalyzed by enzymes
Glucose 2 Pyruvate
(six carbons) (three carbons)
ATPUniversal Energy Currency
• ATP is earned in reactions that yield energy, and
spent in reactions that require it
P P P
ribose
adenine
Mitochondrial Reactions
• Reactions begin when pyruvate enters a mitochondrion
How Cells Make ATP
• Step 3: Electron transport produces many ATP molecules.
– The final stage of cellular
respiration occurs in the
electron transport
systems embedded in
the inner membranes
(cristae) of the mitochondrion.
Glucose
ATP
ATP
ATP
ATP
ADP
ADP
P
P P
P P
Energy in (2 ATP)
Net Energy Yield: 2
PGAL:
pyruvate
NAD+ NAD+
NADH NADH
Intermediates donate phosphate to ADP, making 4
To second set of
reactions
CYTOPLASM
MITOCHONDRION
GLYCOLYSIS
ELECTRON TRANSPORT
PHOSPHORYLATION
KREBS CYCLE ATP
ATP
energy input to start reactions
2 CO2
4 CO2
2
32
water
2 NADH
8 NADH
2 FADH2
2 NADH 2 pyruvate
e- + H+
e- + oxygen
(2 ATP net)
glucose
TYPICAL ENERGY YIELD: 36 ATP
e-
e- + H+
e- + H+
ATP
H+
e- + H+
ATP2 4
Overview of Aerobic Respiration
C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water
dioxide
Creating an H+ Gradient
NADH
OUTER COMPARTMENT
INNER COMPARTMENT
Making ATP
ATP
ADP+Pi
INNER COMPARTMENT
How Electron Transport Forms ATP
©2005 Brooks/Cole - Thomson
Krebs Cycle
NADH
NADH
NADH
ATP ATP
ATP
ATP
ADP + Pi
INNER COMPARTMENT
OUTER COMPARTMENT
acetyl-CoA
free oxygen
6 H+ flows back into inner compartment, through ATP synthases. Flow drives ATP formation.
1 Pyruvate from cytoplasm enters inner mitochondrial compartment.
3 NADH and FADH2 give up electrons and H+ to electron transport systems.
2 Krebs cycle and preparatory steps: NAD+ and FADH2
accept electrons and hydrogen. ATP forms. Carbon dioxide forms.
5 Oxygen accepts electrons, joins with H+ to form water.
4 As electrons move through the transport system, H+ is pumped to outer compartment.
Summary of Energy Harvest(per molecule of glucose)
• Glycolysis– 2 ATP formed by substrate-level phosphorylation
• Krebs cycle and preparatory reactions– 2 ATP formed by substrate-level phosphorylation
• Electron transport phosphorylation– 32 ATP formed
Diffusion
Click to view animation.
Animation
Factors Affecting Diffusion Rate
• Concentration gradient
• Molecular size
• Temperature
• Electrical or pressure gradients
selectively permeable membranebetween two compartments
proteinmolecule
watermolecule
Osmosis
98% water2% sucrose
100% water(distilled)
90% water10% sucrose
98% water2% sucrose
HYPOTONICCONDITIONS
HYPERTONICCONDITIONS
ISOTONICCONDITIONS
Enzyme Structure and Function
• Enzymes speed the rate at which certain reactions occur
• Nearly all are proteins
• An enzyme recognizes and binds to only certain substrates
• Reactions do not alter or use up enzyme molecules
Participants in Metabolic Pathways
• Enzymes
• Energy Carriers
• Cofactors
• Substrates
• Intermediates
• End Products
Factors Influencing Enzyme Activity
Temperature
pH
Salt concentration
Coenzymes and cofactors
productmolecule
©2005 Brooks/Cole - Thomson
two substrate molecules
active site
substratescontactingactive siteof enzyme
substrates briefly bindtightly to enzyme active site
enzyme unchanged by the reaction