Enzymes are necessary because they cause reactions to happen.

transcript

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

• 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

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.

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

glucose

• 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!

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

• 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)

Germinatingseed

Pollentube

Stigma

Pollengrains

Pollentube

Dischargedsperm nuclei (n)

Eggnucleus (n)

Mature flower onsporophyte plant(2n)

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)

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.

Polarnuclei

Pollen grain

Pollen tube

2 sperm

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

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

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

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)

+ + + + + + + ++ + + + + + +

– – – – – – – ––– – – – –

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+

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

RepolarizationK+ flows out

ThresholdHyperpolarization(undershoot)

Resting potential Resting1

• 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

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

Hormone(testosterone)

Receptorprotein

Hormone-receptorcomplex

New protein

LE 11-7b

Signalmolecule

a Helix in themembrane

Signal-binding site

Tyr Tyr

TyrTyrosines

Receptor tyrosinekinase proteins(inactive monomers)CYTOPLASM

Tyr Tyr

Activated tyrosine-kinase regions(unphosphorylateddimer)

Signalmolecule

Fully activated receptor tyrosine-kinase(phosphorylateddimer)

Tyr Tyr

TyrPPP

PPPATP 6 ADP

Tyr Tyr

TyrPPP

Inactiverelay proteins

Cellularresponse 2

Cellularresponse 1

Activated relay proteins

LE 11-10

ATPSecondmessenger

First messenger(signal moleculesuch as epinephrine)

G-protein-linkedreceptor

G proteinAdenylylcyclase

Proteinkinase A

Cellular responses

LE 11-8Signal molecule

Activated relaymolecule

Receptor

Inactiveprotein kinase

1 Activeprotein kinase

Inactiveprotein

Activeprotein

Cellularresponse

Phosphorylation cascade

ADPATP

• All populations will increase continuously, regardless of outside factors.

Survivorship curves

• Generalized strategiesWhat do these graphs tell about survival & strategy of a species?

Human(type I)

Hydra(type II)

Oyster(type III)10

Percent of maximum life span

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

1.0N Exponential growth

Logistic growth

1.0N1,500 N

K 1,500

0 5 10 150

Number of generations

Enzymes are necessary because they cause reactions to happen.

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