enzymes are necessary because they cause reactions to happen
TRANSCRIPT
Enzymes are necessary because they cause reactions to happen.
Metabolism• Chemical reactions of life
– forming bonds between molecules• dehydration synthesis• synthesis• anabolic reactions
– breaking bonds between molecules• hydrolysis• digestion• catabolic reactions
That’s why they’re calledanabolic steroids!
Examples dehydration synthesis (synthesis)
hydrolysis (digestion)
enzyme
enzyme
• Enzymes work by decreasing the potential energy difference between reactant and product
Catalysts• So what’s a cell got to do to reduce
activation energy?– get help! … chemical help… ENZYMES
G
Call in the ENZYMES!
• As a result of its involvement in a reaction, an enzyme permanently alters its shape.
Enzymes vocabularysubstrate
• reactant which binds to enzyme• enzyme-substrate complex: temporary association
product • end result of reaction
active site • enzyme’s catalytic site; substrate fits into active site
substrate
enzyme
productsactive site
Properties of enzymes• Reaction specific
– each enzyme works with a specific substrate • chemical fit between active site & substrate
– H bonds & ionic bonds
• Not consumed in reaction– single enzyme molecule can catalyze thousands or
more reactions per second• enzymes unaffected by the reaction
• Affected by cellular conditions– any condition that affects protein structure
• temperature, pH, salinity
• If a patient in a hospital was accidentally given an IV full of pure water they would be fine because pure water is neutral so it can’t hurt us.
freshwater balanced saltwater
Managing water balance• Cell survival depends on balancing water
uptake & loss
Aquaporins• Water moves rapidly into & out of cells
– evidence that there were water channels• protein channels allowing flow of water across cell
membrane
1991 | 2003
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
Cell (compared to beaker) hypertonic or hypotonic
Beaker (compared to cell) hypertonic or hypotonicWhich way does the water flow? in or out of cell
.05 M .03 M
Do you understand Osmosis…
• Cellular respiration is only done by heterotrophs because autotrophs can make their own energy.
NPK
…
H2O
What does it mean to be a plant?• Need to…
– collect light energy• transform it into chemical energy
– store light energy• in a stable form to be moved around
the plant or stored – need to get building block atoms
from the environment • C,H,O,N,P,K,S,Mg
– produce all organic molecules needed for growth• carbohydrates, proteins, lipids, nucleic acids
ATP
glucose
CO2
• The purpose of fermentation is to produce a small amount of energy when cells don’t have access to oxygen.
recycleNADH
Alcohol Fermentation
1C3C 2Cpyruvate ethanol + CO2
NADH NAD+
Count thecarbons!
Dead end process at ~12% ethanol, kills
yeast can’t reverse the
reaction
bacteria yeast
back to glycolysis
recycleNADH
Reversible process once O2 is available,
lactate is converted back to pyruvate by the liver
Lactic Acid Fermentationpyruvate lactic acid
3C 3CNADH NAD+
Count thecarbons!
O2
animalssome fungi
back to glycolysis
• Plants use water only as a means of keeping their cells full and holding the plant itself upright.
ETC of Photosynthesis
Chloroplasts transform light energy into chemical energy of ATP
use electron carrier NADPH
generates O2
• The second step of photosynthesis is called the dark reactions because it only happens in the dark.
Light: absorption spectra• Photosynthesis gets energy by absorbing wavelengths of light
– chlorophyll a • absorbs best in red & blue wavelengths & least in green
– accessory pigments with different structures absorb light of different wavelengths
• chlorophyll b, carotenoids, xanthophylls
Why areplants green?
From Light reactions to Calvin cycle
• Calvin cycle – chloroplast stroma
• Need products of light reactions to drive synthesis reactions– ATP– NADPH
stroma
thylakoid
ATP
• Diagram how a gamete with 3 chromosomes could be produced with two maternal chromosomes and one paternal chromosome. (there isn’t anything wrong in this statement)
• One trait = one gene
• All proteins are made of enzymes.
Proteins • Most structurally & functionally diverse group• Function: involved in almost everything
– enzymes (pepsin, DNA polymerase)– structure (keratin, collagen)– carriers & transport (hemoglobin, aquaporin)– cell communication
• signals (insulin & other hormones) • receptors
– defense (antibodies) – movement (actin & myosin)– storage (bean seed proteins)
• Structural homologies only exist in animals, never in plants.
• When the environment changes all species living in it will change to adapt to it.
• Whales lost their hind limbs because they stopped using them.
Homologous structures• Similar structure• Similar development• Different functions • Evidence of close
evolutionary relationship– recent common ancestor
Analogous structures Separate evolution of structures
similar functions similar external form different internal structure & development different origin no evolutionary relationship
Solving a similar problem with a similar solution
Don’t be fooledby their looks!
Convergent evolution• Flight evolved in 3 separate animal groups
– analogous structures
Does this mean they have a recent common ancestor?
Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals
similar adaptations to life in the sea
not closely related
Those fins & tails & sleek bodies areanalogous structures!
• Bird and bat wings can only be described as homologous structures, not as analogous structures.
• The strongest evidence supporting the endosymbiotic theory is that mitochondria and bacteria are the same size and have a similar shape.
• The primitive atmosphere had to contain oxygen before life could evolve.
• Plants are simple organisms with no tissues or organs.
Plant TISSUES• Dermal
– epidermis (“skin” of plant)– single layer of tightly packed
cells that covers & protects plant
• Ground– bulk of plant tissue – photosynthetic mesophyll,
storage • Vascular
– transport system in shoots & roots
– xylem & phloem
Basic plant anatomy 3• root
– root tip– root hairs
• shoot (stem)– nodes
• internodes– buds
• terminal or apical buds• axillary buds• flower buds & flowers
• leaves– mesophyll tissue– veins (vascular bundles)
• Plants actively move water up their trunks.
Transport in plants• H2O & minerals
– transport in xylem – Transpiration
• Adhesion, cohesion & Evaporation
• Sugars– transport in phloem– bulk flow
• Gas exchange– photosynthesis
• CO2 in; O2 out• stomates
– respiration• O2 in; CO2 out• roots exchange gases within
air spaces in soil
Why doesover-wateringkill a plant?
Ascent of xylem fluidTranspiration pull generated by leaf
• Plants get food from the ground.
On a plant…What’s a source…What’s a sink?
can flow 1m/hr
Pressure flow in phloem• Mass flow hypothesis
– “source to sink” flow• direction of transport in phloem is
dependent on plant’s needs
– phloem loading• active transport of sucrose
into phloem• increased sucrose concentration
decreases H2O potential
– water flows in from xylem cells• increase in pressure due to increase in
H2O causes flow
Transport of sugars in phloem• Loading of sucrose into phloem
– flow through cells via plasmodesmata– proton pumps
• cotransport of sucrose into cells down proton gradient
• Plants do not do sexual reproduction.
The life cycle of an angiosperm
Nucleus ofdevelopingendosperm (3n)
Zygote (2n)
FERTILIZATION
Embryo (2n)
Endosperm(foodsupply) (3n)
Seed coat (2n)
Seed
Germinatingseed
Pollentube
Sperm
Stigma
Pollengrains
Pollentube
Style
Dischargedsperm nuclei (n)
Eggnucleus (n)
Mature flower onsporophyte plant(2n)
Key
Haploid (n)
Diploid (2n)
Anther
Ovule withmegasporangium (2n)
Male gametophyte(in pollen grain)
Microspore (n)
MEIOSIS
MicrosporangiumMicrosporocytes (2n)
MEIOSIS
Generative cell
Tube cell
Survivingmegaspore(n)
Ovary
Megasporangium(n)
Female gametophyte(embryo sac)
Antipodal cellsPolar nucleiSynergidsEgg (n)
Pollentube
Sperm(n)
Growth of the pollen tube and double fertilization
If a pollen graingerminates, a pollen tube
grows down the styletoward the ovary.
Stigma
The pollen tubedischarges two sperm into
the female gametophyte(embryo sac) within an ovule.
One sperm fertilizesthe egg, forming the zygote.
The other sperm combines withthe two polar nuclei of the embryo
sac’s large central cell, forminga triploid cell that develops into
the nutritive tissue calledendosperm.
1
2
3
Polarnuclei
Egg
Pollen grain
Pollen tube
2 sperm
Style
Ovary
Ovule (containingfemale Gametophyte, orEmbryo sac)
Micropyle
OvulePolar nucleiEgg
Two spermabout to bedischarged
Endosperm nucleus (3n) (2 polar nuclei plus sperm)
Zygote (2n)(egg plus sperm)
Seed structure
(a) Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates.
(b) Castor bean, a eudicot with thin cotyledons. The narrow, membranous cotyledons (shown in edge and flat views) absorb food from the endosperm when the seed germinates.
(c) Maize, a monocot. Like all monocots, maize has only one cotyledon. Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root.
Seed coat
Radicle
Epicotyl
Hypocotyl
Cotyledons
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
Scutellum(cotyledon)
Coleoptile
Coleorhiza
Pericarp fusedwith seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
• Ectotherms do not regulate their body temperature in any way
• Most materials are transported through the blood stream of mammals and into and out of tissues by active transport.
Arranged as a Phospholipid bilayer
polarhydrophilicheads
nonpolarhydrophobictails
polarhydrophilicheads
• Serves as a cellular barrier / borderH2Osugar
lipids
salt
waste
impermeable to polar molecules
Proteins domains anchor molecule• Within membrane
– nonpolar amino acids • hydrophobic • anchors protein
into membrane
• On outer surfaces of membrane in fluid– polar amino acids
• hydrophilic• extend into extracellular
fluid & into cytosol
Polar areasof protein
Nonpolar areas of protein
Many Functions of Membrane ProteinsOutside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
“Antigen”
“Channel”
Membrane Proteins• Proteins determine membrane’s specific functions
– cell membrane & organelle membranes each have unique collections of proteins
• Classes of membrane proteins:– peripheral proteins
• loosely bound to surface of membrane• ex: cell surface identity marker (antigens)
– integral proteins • penetrate lipid bilayer, usually across whole membrane • transmembrane protein• ex: transport proteins
– channels, pumps
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
• In each of the following pairs the two terms given mean the same thing and do the same job.– leukocyte; lymphocyte– antigen; antibody– B lymphocyte; T lymphocyte– cytotoxic T cell; helper T cell
1st line: Non-specific External defense
• Barrier• skin
• Traps• mucous membranes, cilia,
hair, earwax
•Elimination• coughing, sneezing, urination, diarrhea
•Unfavorable pH• stomach acid, sweat, saliva, urine
•Lysozyme enzyme• digests bacterial cell walls• tears, sweat
Lining of trachea: ciliated cells & mucus secreting cells
Leukocytes: Phagocytic WBCs • Attracted by chemical signals released by damaged
cells – ingest pathogens– digest in lysosomes
• Neutrophils– most abundant WBC (~70%)– ~ 3 day lifespan
• Macrophages– “big eater”, long-lived
• Natural Killer Cells– destroy virus-infected cells
& cancer cells
• Natural Killer Cells perforate cells– release perforin protein– insert into membrane of target cell– forms pore allowing fluid to
flow in & out of cell– cell ruptures (lysis)
• apoptosis
Destroying cells gone bad!
perforin puncturescell membrane
cell membrane
natural killer cell
cell membrane
virus-infected cell
vesicle
perforin
• Specific defense with memory – lymphocytes
• B cells• T cells
– antibodies • immunoglobulins
• Responds to…– antigens
• cellular name tags– specific pathogens – specific toxins– abnormal body cells (cancer)
3rd line: Acquired (active) Immunity
B cell
“self” “foreign”
How are invaders recognized?• Antigens
– cellular name tag proteins• “self” antigens
– no response from WBCs
• “foreign” antigens – response from WBCs– pathogens: viruses, bacteria, protozoa, parasitic worms, fungi,
toxins – non-pathogens: cancer cells, transplanted tissue, pollen
Lymphocytes • B cells– mature in bone marrow– humoral response system
• attack pathogens still circulating in blood & lymph
– produce antibodies• T cells
– mature in thymus– cellular response system
• attack invaded cells
• “Maturation”– learn to distinguish “self”
from “non-self” antigens • if react to “self” antigens, cells
are destroyed during maturation
bone marrow
Antibodies • Proteins that bind to a specific antigen– multi-chain proteins – binding region matches molecular shape of antigens– each antibody is unique & specific
• millions of antibodies respond to millions of foreign antigens
– tagging “handcuffs”• “this is foreign…gotcha!”
each B cell has ~50,000
antibodies
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YY
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YYY
Y
antigenantigen-binding site on antibody
variable binding region
Vaccinations • Immune system exposed
to harmless version of pathogen – stimulates B cell system to produce
antibodies to pathogen• “active immunity”
– rapid response on future exposure– creates immunity
without getting disease!
• Most successful against viruses
Attack of the Killer T cells
Killer T cellbinds to
infected cell
• Destroys infected body cells– binds to target cell– secretes perforin protein
• punctures cell membrane of infected cell– apoptosis
infected celldestroyed
cell membrane
Killer T cell
cell membrane
target cell
vesicle
perforin puncturescell membrane
• Blood and filtrate move in the same direction through the nephrons of the kidney and this helps conserve energy.
Osmotic control in nephron• How is all this re-absorption achieved?
– tight osmotic control to reduce the energy cost of excretion
– use diffusion instead of active transportwherever possible
the value of acounter current exchange system
Summary • Not filtered out
– cells u proteins– remain in blood (too big)
• Reabsorbed: active transport– Na+ u amino acids– Cl– u glucose
• Reabsorbed: diffusion– Na+ u Cl–
– H2O• Excreted
– urea– excess H2O u excess solutes (glucose, salts)– toxins, drugs, “unknowns”
whyselective reabsorption
& not selectivefiltration?
• Neurons are at equilibrium at resting potential.
Nervous system cells
dendrites
cell body
axon
synaptic terminal
Neuron a nerve cell
Structure fits function many entry points for
signal one path out transmits signal
signal direction
signaldirection
dendrite cell body axon synapse
myelin sheath
Cells have voltage!• Opposite charges on opposite sides of cell
membrane– membrane is polarized
• negative inside; positive outside• charge gradient• stored energy (like a battery)
+ + + + + + + ++ + + + + + +
+ + + + + + + ++ + + + + + +
– – – – – – – ––– – – – –
– – – – – – – ––– – – – –
Gate
+ –
+
+
channel closed
channel open
How does a nerve impulse travel?• Wave: nerve impulse travels down neuron
– change in charge opens next Na+ gates down the line • “voltage-gated” channels
– Na+ ions continue to diffuse into cell– “wave” moves down neuron = action potential
– – + + + + + +– + + + + + +
– – + + + + + +– + + + + + +
+ + – – – – – –+ – – – – – –
+ + – – – – – –+ – – – – – –Na+
wave
The restof thedominoes fall!
1. Resting potential2. Stimulus reaches threshold
potential3. Depolarization
Na+ channels open; K+ channels closed
4. Na+ channels close; K+ channels open
5. Repolarizationreset charge gradient
6. UndershootK+ channels close slowly
Action potential graph
–70 mV–60 mV
–80 mV
–50 mV–40 mV–30 mV–20 mV–10 mV
0 mV10 mV Depolarization
Na+ flows in
20 mV30 mV
40 mV
RepolarizationK+ flows out
ThresholdHyperpolarization(undershoot)
Resting potential Resting1
2
3
4
5
6
Mem
bran
e po
tenti
al
• The nervous and endocrine systems send completely different kinds of messages so they never work together.
axon terminal
synaptic vesicles
muscle cell (fiber)
neurotransmitteracetylcholine (ACh)receptor protein
Ca++
synapse
action potential
Chemical synapse Events at synapse
action potential depolarizes membrane opens Ca++ channels neurotransmitter vesicles fuse with
membrane release neurotransmitter to synapse
diffusion neurotransmitter binds with protein
receptor ion-gated channels open
neurotransmitter degraded or reabsorbed
We switched…from an electrical signalto a chemical signal
LE 11-4
Paracrine signaling
Local regulatordiffuses throughextracellular fluid
Secretoryvesicle
Secretingcell
Target cell
Local signaling
Electrical signalalong nerve celltriggers release ofneurotransmitter
Neurotransmitter diffuses across synapse
Endocrine cell Bloodvessel
Long-distance signaling
Hormone travelsin bloodstreamto target cells
Synaptic signaling
Target cellis stimulated
Hormonal signaling
Target cell
• All hormones have the same types of effects on cells, no matter what they are made of.
LE 11-5_3
EXTRACELLULARFLUID
Reception
Plasma membrane
Transduction
CYTOPLASM
Receptor
Signalmolecule
Relay molecules in a signal transductionpathway
Response
Activationof cellularresponse
LE 11-6
EXTRACELLULARFLUID
Plasmamembrane
The steroidhormone testosteronepasses through theplasma membrane.
Testosterone bindsto a receptor proteinin the cytoplasm,activating it.
The hormone-receptor complexenters the nucleusand binds to specificgenes.
The bound proteinstimulates thetranscription ofthe gene into mRNA.
The mRNA istranslated into aspecific protein.
CYTOPLASM
NUCLEUS
DNA
Hormone(testosterone)
Receptorprotein
Hormone-receptorcomplex
mRNA
New protein
LE 11-7b
Signalmolecule
a Helix in themembrane
Signal-binding site
Tyr
Tyr
Tyr Tyr
Tyr
TyrTyrosines
Receptor tyrosinekinase proteins(inactive monomers)CYTOPLASM
Tyr
Tyr
Tyr Tyr
Tyr
Tyr Tyr
Tyr
Tyr Tyr
Tyr
Tyr
Tyr
Tyr
Tyr Tyr
Tyr
Tyr
Activated tyrosine-kinase regions(unphosphorylateddimer)
Signalmolecule
Dimer
Fully activated receptor tyrosine-kinase(phosphorylateddimer)
Tyr
Tyr
Tyr Tyr
Tyr
TyrPPP
PPPATP 6 ADP
Tyr
Tyr
Tyr Tyr
Tyr
TyrPPP
PPP
Inactiverelay proteins
Cellularresponse 2
Cellularresponse 1
Activated relay proteins
6
LE 11-10
cAMP
ATPSecondmessenger
First messenger(signal moleculesuch as epinephrine)
G-protein-linkedreceptor
G proteinAdenylylcyclase
Proteinkinase A
Cellular responses
GTP
LE 11-8Signal molecule
Activated relaymolecule
Receptor
Inactiveprotein kinase
1 Activeprotein kinase
1
Inactiveprotein kinase
2 Activeprotein kinase
2
Inactiveprotein kinase
3 Activeprotein kinase
3
ADP
Inactiveprotein
Activeprotein
Cellularresponse
Phosphorylation cascade
ATP
PPP i
ADPATP
PPP i
ADPATP
PPP i
P
P
P
• All populations will increase continuously, regardless of outside factors.
Survivorship curves
• Generalized strategiesWhat do these graphs tell about survival & strategy of a species?
0 25
1000
100
Human(type I)
Hydra(type II)
Oyster(type III)10
150
Percent of maximum life span
10075
Surv
ival
per
thou
sand
I. High death rate in post-reproductive years
II. Constant mortality rate throughout life span
III. Very high early mortality but the few survivors then live long (stay reproductive)
Reproductive strategies• K-selected
– late reproduction– few offspring– invest a lot in raising offspring
• primates• coconut
• r-selected– early reproduction– many offspring– little parental care
• insects• many plants
K-selected
r-selected
K =carryingcapacity
Logistic rate of growth• Can populations continue to grow
exponentially? Of course not!
effect of natural controls
no natural controls
What happens as N approaches K?
Population growth predicted by the logistic model
dNdt
1.0N Exponential growth
Logistic growth
dNdt
1.0N1,500 N
1,500
K 1,500
0 5 10 150
500
1,000
1,500
2,000
Number of generations
Popu
latio
n si
ze (N
)