Other Other

Metabolic Metabolic

PathwaysPathways

Fats Glycogen Protein

The body fat is our major source of stored energy

• Our adipose tissue is made of fat cells adipocytes.

• A typical 70 kg person has about 135 000 kcal of energy stored as fat, 24 000 kcal as protein, 720 kcal as glycogen reserves, and 80 kcal as blood reserves, and 80 kcal as blood glucose.

• The energy available from stored fats is about 85 % of the total energy available in the body.

Lipolysis via β-oxidation

Lipases

Beta-oxidation of fatty acids

• β-oxidation of FA produces acetyl CoA

and NADH and FADH2, which are

sources of energy (ATP)

• First, FA are converted to acyl CoA in the

cytoplasm:

Carnitine shuttle

• For transport into mitochondria, CoA is replaced with carnitineby acylcarnitine transferase I

• Inside mitochondria a corresponding enzyme (II) forms acyl CoA

• Malonyl CoA inhibits acylcarnitine transferase I

• So, when FA synthesis is active, FA are not transported into mitochondria

• Defects in FA transport (including carnitine deficiency) are known

Beta-Oxidation of Fatty Acids

In reaction 1, oxidation:

• Removes H atoms from

the αααα and ββββ carbons.

ββββ αααα

the αααα and ββββ carbons.

• Forms a trans C=C bond.

• Reduces FAD to FADH2.

Beta-Oxidation of Fatty Acids

In reaction 2, hydration:

• Adds water across the

trans C=C bond.

ββββ αααα

trans C=C bond.

• Forms a hydroxyl group

(—OH) on the ββββ carbon.

Beta (ββββ)-Oxidation of Fatty Acids

In reaction 3, a

second oxidation:

• Oxidizes the hydroxyl

ββββ αααα

• Oxidizes the hydroxyl

group.

• Forms a keto group

on the ββββ carbon.

Beta (ββββ)-Oxidation of Fatty Acids

In Reaction 4, acetyl CoA is cleaved:

• By splitting the bond • By splitting the bond between the αααα and ββββcarbons.

• To form a shortened fatty acyl CoA that repeats steps 1 - 4 of ββββ-oxidation.

Beta (ββββ)-Oxidation of Myristic (C14) Acid

Beta (ββββ)-Oxidation of Myristic (C14) Acid

(continued)

7 Acetyl

CoA6 cycles

ββββ-oxidação dos ácidos gordos – uma via em espiral

Cycles of β-Oxidation

The length of a fatty acid:

• Determines the number of oxidations and

• The total number of acetyl CoA groups.

Carbons in Acetyl CoA ββββ-Oxidation CyclesCarbons in Acetyl CoA ββββ-Oxidation Cycles

Fatty Acid (C/2) (C/2 –1)

12 6 5

14 7 6

16 8 7

18 9 8

β-Oxidation and ATP

Activation of a fatty acid requires:

• 2 ATP

One cycle of oxidation of a fatty acid produces:

• 1 NADH 3 ATP

• 1 FADH 2 ATP• 1 FADH2 2 ATP

Acetyl CoA entering the citric acid cycle produces:

• 1 Acetyl CoA 12 ATP

ATP for Lauric Acid C12

ATP production for lauric acid (12 carbons):

Activation of lauric acid -2 ATP

6 Acetyl CoA6 acetyl CoA x 12 ATP/acetyl CoA 72 ATP

5 Oxidation cycles5 NADH x 3ATP/NADH 15 ATP

5 FADH2 x 2ATP/FADH2 10 ATP

Total 95 ATP

Oxidation of Unsaturated Fatty Acids.

• Oxidation of monounsaturated fatty acyl-CoA requires additional reaction performed with the help of the enzyme isomerase.

• Double bonds in the unsaturated fatty acids are in the cis configuration and cannot be acted upon by enoyl-CoA hydratase (the enzyme in the cis configuration and cannot be acted upon by enoyl-CoA hydratase (the enzyme catalyzing the addition of water to the trans double bond generated during β-oxidation.

• Enoyl-CoA isomerase repositions the double bond, converting the cis isomer to trans isomer, a normal intermediate in β-oxidation.

Protein Catabolism

Proteins are degraded into amino acids

Ammonium ion is converted

to urea in most mammals

The liver is the major site of protein degradation in mammals

First step in protein

degradation is the

removal of the nitrogen

Catabolism of proteins:

-amino acids undergo deamination to remove the amino

group

-remainder of the amino acid is converted to a molecule

that enters glycolysis or the Krebs cycle

Protein Catabolism

that enters glycolysis or the Krebs cycle

-for example:

alanine is converted to pyruvate

aspartate is converted to oxaloacetate

Amino acid Catabolism

• Almost all plants are photosynthetic autotrophs, as

are some bacteria and protists– Autotrophs generate their own organic matter through

photosynthesis

– Sunlight energy is transformed to energy stored in the form of

chemical bonds

THE BASICS OF PHOTOSYNTHESIS

(a) Mosses, ferns, andflowering plants

(b) Kelp

(c) Euglena (d) Cyanobacteria

Light Energy Harvested by Plants &

Other Photosynthetic Autotrophs

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Photosynthesis is the process by which autotrophic organisms use light

energy to make sugar and oxygen gas from carbon dioxide and water

6CO2 6H2O C6H12O6 6O2lightenergy

→→→→+ ++

Experimental evidence

• Where did the O2 come from?

– radioactive tracer = O18

6CO2 6H2OC6H12O6 6O2

lightenergy

→→→→+ ++

Experiment 1

energyenergy

6CO2 6H2OC6H12O6 6O2

lightenergy

→→→→+ ++

Experiment 2

Proved O2 came from H2O not CO2 = plants split H2O

Water is oxidized

Carbon dioxide is reduced

• Chloroplasts

absorb light

energy and

convert it to

LightReflected

light

THE COLOR OF LIGHT SEEN IS THE

COLOR NOT ABSORBED

convert it to

chemical energy

Absorbedlight

Transmittedlight

Chloroplast

Blue and red

wavelengths are

absorved

WHYWHY AREARE PLAPLANTS NTS GREGREEN?EN?

Plant Cells

have Green

Chloroplasts

The thylakoid

membrane of the

chloroplast is

impregnated with

photosynthetic

pigments (i.e.,

chlorophylls,

carotenoids).

Chloroplasts: Sites of Photosynthesis

• Photosynthesis

– Occurs in chloroplasts, organelles in certain

plants

– All green plant parts have chloroplasts and

carry out photosynthesiscarry out photosynthesis

• The leaves have the most chloroplasts

• The green color comes from chlorophyll in the

chloroplasts

• The pigments absorb light energy

• In most plants, photosynthesis occurs

primarily in the leaves, in the chloroplasts

• A chloroplast contains:

– stroma, a fluid

Photosynthesis occurs in chloroplasts

– stroma, a fluid

– grana, stacks of thylakoids

• The thylakoids contain chlorophyll

– Chlorophyll is the green pigment that captures

light for photosynthesis

The location and structure of chloroplasts

LEAF CROSS SECTION MESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

ThylakoidcompartmentThylakoidStroma

Granum

StromaGrana

Chloroplast Pigments• Chloroplasts contain several pigments

– Chlorophyll a

– Chlorophyll b

– Carotenoids

(carotenes and xanthophylls)

Chlorophyll a and b

CHO in chlorophyll b

Phyto tail

Different pigments absorb light differently

Violet

Blue

Red

Orange

Green

Yellow

• Is only pigment that directly participates in the light reactions

• Other pigments add energy to chlorophyll a or dissipate excessive light

energy

• Absorption of light elevates an electron to a higher energy orbital

(increased potential energy)

Chlorophyll a

• The Calvin cycle makes

sugar from carbon dioxide

Light

Chloroplast

Lightreactions

Calvincycle

NADP++++

ADP+ P

• The light reactions

convert solar energy to

chemical energy

– Produce ATP & NADPH

AN OVERVIEW OF PHOTOSYNTHESIS

sugar from carbon dioxide

– ATP generated by the light

reactions provides the energy

for sugar synthesis

– The NADPH produced by the

light reactions provides the

electrons for the reduction of

carbon dioxide to glucose

reactionscycle

• Two connected photosystems collect photons of

light and transfer the energy to chlorophyll

electrons

In the light reactions, electron transport In the light reactions, electron transport

chains generate ATP, NADPH, & Ochains generate ATP, NADPH, & O22

• The excited electrons are passed from the primary

electron acceptor to electron transport chains

– Their energy ends up in ATP and NADPH

Photosystems

• Collection of pigments and

proteins found associated

with the thylakoid

membrane that harness

the energy of an excited

electron to do work

• Captured energy is

transferred between

photosystem molecules

until it reaches the

chlorophyll molecule at the

reaction center

What Next?

• At the reaction center are

2 molecules

– Chlorophyll a

– Primary electron

acceptor

• The reaction-center • The reaction-center

chlorophyll is oxidized as

the excited electron is

removed through the

reduction of the primary

electron acceptor

• Photosystem I and II

Electron Flow• Two routes for the path of electrons stored in the primary

electron acceptors

• Both pathways

– begin with the capturing of photon energy

– utilize an electron transport chain with cytochromes for

chemiosmosis

• Noncyclic electron flow

– uses both photosystem II and I

– electrons from photosystem II are removed and replaced by

electrons donated from water

– synthesizes ATP and NADPH

– electron donation converts water into ½ O2 and 2H+

• Cyclic electron flow

– Uses photosystem I only

– electrons from photosystem I are recycled

– synthesizes ATP only

Photophosphorylation

cyclic

photophosphorylation

noncyclic

photophosphorylation

Noncyclic Photophosphorylation• Photosystem II regains electrons by splitting water, leaving

O2 gas as a by-product

Primaryelectron acceptor

Primaryelectron acceptor

Photons

PHOTOSYSTEM I

PHOTOSYSTEM II

Energy forsynthesis of

by chemiosmosis

Noncyclic Electron FlowElectrons at reaction-center

are energized

H2O split via enzyme

catalysed reaction forming 2H+,

2e-, and 1/2 O2. Electrons move

to fill orbital vacated by removed

electrons

Each excited electron is passed

along an electron transport chain

fueling the chemiosmotic

synthesis of ATP

The electrons are now lower in

energy and enters photosystem I

via plastocyanin (PC) where they

are re-energized

The electrons are then passed

to a different electron transport

system that includes the iron

containing protein ferridoxin.

The enzyme NADP+ reductase

assists in the oxidation of ferridoxin

and subsequent reduction of

NADP+ to NADPH

• The electron transport chains are arranged

with the photosystems in the thylakoid

membranes and pump H+ through that

membrane

Chemiosmosis powers ATP synthesis

in the light reactions

membrane

– The flow of H+ back through the membrane is

harnessed by ATP synthase to make ATP

– In the stroma, the H+ ions combine with NADP+

to form NADPH

• The production of ATP by chemiosmosis in

photosynthesis

Thylakoidcompartment(high H+)

Thylakoid

Light Light

Thylakoidmembrane

Stroma(low H+)

Antennamolecules

ELECTRON TRANSPORT

CHAIN

PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

Where are the photosystems found on

the thylakoid membrane?

Chemiosmosis in 2 Organelles

Both the Mitochondria and Chloroplast

generate ATP via a proton motive force

resulting from an electrochemical

imbalance across a membrane

Both utilize an electron transport chain

primarily composed of cytochromes to

pump H+ across a membrane.

Both use a similar ATP synthase

complex

Source of “fuel” for the process differs

Calvin Cycle

• Starts with CO2 and produces Glyceraldehyde 3-phosphate

• Three turns of Calvin cycle generates one molecule of product

• Three phases to the process: I) Carbon Fixation; II) Reduction of CO2; III)

Regeneration of RuBP

A molecule of CO2 is converted

from its inorganic form to an

organic molecule (fixation)

through the attachment to a 5C

sugar (ribulose bisphosphate or

RuBP).

Phase 1

Calvin Cycle

–Catalysed by the enzyme

RuBP carboxylase (Rubisco).

The formed 6C sugar

immediately cleaves into 3-

phosphoglycerate

Each 3-phosphoglycerate

molecule receives an

additional phosphate group

forming 1,3-

Bisphosphoglycerate (ATP

phosphorylation)

Phase 2

Calvin Cycle

phosphorylation)

•NADPH is oxidized and the

electrons transferred to

1,3-Bisphosphoglycerate

cleaving the molecule as it

is reduced forming

Glyceraldehyde 3-

phosphate

Phase 3

The final phase of the

cycle is to regenerate

RuBP

•Glyceraldehyde 3-

phosphate is converted

Calvin Cycle

phosphate is converted

to RuBP through a series

of reactions that involve

the phosphorylation of

the molecule by ATP

Variations Anyone?

• In hot/arid regions plants may run

short of CO2 as a result of water

conservation mechanisms

• C4 Photosynthesis

CO2 may be captured by

conversion of PEP

(Phosphoenolpyruvate) into (Phosphoenolpyruvate) into

oxaloacetate and ultimately malate

that is exported to cells where the

Calvin cycle is active

• CAM Photosynthesis

CO2 may be captured as inorganic

acids that my liberate CO2 during

times of reduced availability