metabolism 2

8/2/2019 Metabolism 2

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Metabolism Metabolism is the set of chemical reactions that happen in the cells

of living organisms to sustain life. These processes allow organisms togrow and reproduce, maintain their structures, and respond to their

environments.

Metabolism is usually divided into two categories.

Catabolism: Energy yielding reactions in which complex molecules

are broken down to small molecules. Catabolism produces chemical

ener usuall ATP where it is utilized for various cellular functions:

Synthesis of proteins, RNA, DNA for growth, adaptation and repair.

Synthesis of fats and glycogen.

Performance of mechanical work.

Eg: Cellular respiration.

Anabolism: Energy requiring reactions in which simple precursor

molecules are converted into complex molecules. It requires chemical

energy (usually ATP) which is provided by catabolism. Eg: Synthesis of proteins, nucleic acids etc.


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Catabolism & Anabolism


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Cell metabolism

Energy is the ability to do work.

Living things need to acquire energy; this is a

characteristic of life. Cells use acquired energy to:

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Carry out reactions that allow cells to develop, grow,

and reproduce.

Organisms use enzymes to break down energy-richglucose to release its potential energy.

This energy is trapped and stored in the form of

adenosine triphosphate (ATP).


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Cellular Energy-ATP

Components:

1. adenine: nitrogenous base

2. ribose: five carbon sugar3.phosphate group: chain of 3

-

Last phosphate group (PO4) contains the MOST energy

riboseribose

adenineadenine

P P P

phosphate groupphosphate group


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ATP: Energy for Cells

ATP (adenosine triphosphate) is the energycurrency of cells.

ATP is constantly regenerated from ADP(adenosine diphosphate) after energy isex ended b the cell.

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Use of ATP by the cell has advantages:

1) It can be used in many types of reactions.

2) When ATP ADP + P, energy released issufficient for cellular needs and little energy iswasted.


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Function of ATP Cells make use of ATP for:

Chemical work ATP supplies energy tosynthesize macromolecules, and therefore theorganism.

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Transport work ATP supplies energyneeded to pump substances across the plasmamembrane.

Mechanical work ATP supplies energy forcellular movements.


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Biological Energy Cycle

Food + O2 CO2 + H2O + energy

Chemical Mechanical

60-70% of this energy is heat

The rest is used for

Muscle contraction

Cellular operations (respiration)

Digestion and absorption

Synthesis o new compounds

Glandular function


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Biological Energy Cycle

Cellular Respiration - Theprocess by which cellstransfer energy from foodto ATP in a stepwise

series of reactions; reliesheavily upon the use ofoxygen

naero c - n e a senceof, not requiring, norutilizing oxygen

Aerobic- In the presence

of, requiring, or utilizingoxygen


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Biological Energy production Bioenergetics

The study of energy in living systems (environments) and theorganisms (plants and animals) that utilize them

Energy: Required by all organisms

May be Kinetic or Potential energy

Kinetic Energy: Energy ofMotion

Heat and light energy are examples

Potential Energy: Energy of position

Includes energy stored in chemical bonds


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Two Types of Energy Reactions

Endergonic Reactions:

Chemical reaction that requires a net input ofenergy.

Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

SUNphotons Light Energy

(glucose)

xergon c eact ons :

Chemical reactions that releases energy

Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O+ ATP(glucose)(glucose)

EnergyEnergy


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Dehydration of ATP

ADP + P ATP + H2O (endergonic)

DehydrationDehydration(Remove H(Remove H22OO

P P P

Adenosine triphosphate (ATP)Adenosine triphosphate (ATP)

P P P++

Adenosine diphosphate (ADP)Adenosine diphosphate (ADP)

Energy is restored inchemical bonds


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Hydrolysis of ATP

ATP + H2O ADP + P (exergonic)

P P P

Adenosine triphosphate (ATP)Adenosine triphosphate (ATP)

ATPase

HydrolysisHydrolysis(add water)(add water)

P P P++

Adenosine diphosphate (ADP)Adenosine diphosphate (ADP)

Energy is used by cells


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En ergonic Reaction -

Photosynthesis

Autotrophs produce theirown food (glucose).

Process called photosynthesis.

Mainly occurs in the leaves:

a. stoma - pores

. mesop y ce s

Stoma

Mesophyll

Cell

Chloroplast


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Photosynthesis

Involves the Use Of light Energy

to convert Water (H20) and

Carbon Dioxide (CO2) into Oxygen

(O2) and High Energy

Carbohydrates (sugars, e.g.Glucose) & Starches


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Stomata (stoma)

Pores in a plants cuticle through which water vapor and gases (CO2 &

O2) are exchanged between the plant and the atmosphere.

Oxygen

(O2)

Stoma

Guard CellGuard CellCarbon Dioxide

(CO2)

Found on the underside of leaves


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Mesophyll Cell of Leaf

Cell Wall

Nucleus

Chloroplast

Photosynthesis occurs in these

cells!

Thylakoid stacks are

connected together

GranumThylakoidOuter MembraneInner Membrane

Stroma

Chloroplast Organelle where photosynthesis takes place.


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Chlorophyll

In addition to water,carbon dioxide, and light

energy, photosynthesis requires Pigments

Chlorophyll is the primary light-absorbing pigmentin autotrophs

Located in the thylakoid membranes Chlorophyll have Mg+ in the center

Chlorophyll pigments harvest energy (photons) byabsorbing certain wavelengths (blue-420 nm andred-660 nm are most important)

Plants are green because the green wavelength is

reflected, not absorbed.


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Two Parts of PhotosynthesisTwo reactions make up

photosynthesis:

1.Light Reaction or Light-dependentReaction Produces energy from solar

power (photons) in the form

of ATP and NADPH. Occurs in Thylakoidmembranes

2. Calvin Cycle or Light-independent

Also called Carbon Fixationor C3 Fixation 3-carbon molecule called

Ribulose Biphosphate(RuBP) is used toregenerate the Calvin

cycle Uses energy (ATP and NADPH)

from light reaction to makesugar (glucose).

Occurs in Stroma


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1.Light Reaction or Light-dependent

ReactionThe 'light-dependent reactions', or

photosynthesis, is the first stage of photosynthesis, the process by which plants

ca ture and store ener from sunli ht. In this

process, light energy is converted into chemicalenergy, in the form of the energy-carrying

molecules ATP and NADPH. It occurs in thylakoid

membranes.


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2. Calvin Cycle or Light-independent

Reaction

In the light-independent reactions, the formed

NADPH and ATP drive the reduction of CO2 to moreuseful organic compounds, such as glucose. It also

,

the need of light, for they are driven by ATP and

NADPH, products of light. They are often called the

Calvin Cycle or Carbon fixation. It occurs in stroma.


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Factors Affecting the Rate of Photosynthesis

Amount of available water.

Temperature.

Amount of available light

.


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Cellular RespirationCellular respiration is the set of the metabolic

reactions and processes that take place in the

cells of organisms to convert biochemical energy

from nutrients into adenosine triphosphate (ATP),

.


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Glycolysis

Glycolysis is a metabolic

pathway that is found in the

cytosol of cells in all living

organisms. This pathway

does not require oxygen, and

anaerobic circumstances. The

process converts one

molecule of glucose into two

molecules of pyruvate

(pyruvic acid).

yco ys s


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yco ys sBefore glucose can be converted into ATP, it has be broken down into two pyruvate

molecules (the ionized form of pyruvic acid). This process is known as glycolysis. Glycolysis

takes place in the cytoplasm and can occur without the presence of oxygen and is theprimary energy source for most organisms. This process consumes two ATP molecules, and

produces four ATP molecules and two NADH2+ molecules. Glycolysis is summarized below:

1. Glucose 6-phosphate is formed when the 6th carbon on the glucose molecule is

phosphorylated by an ATP molecule.

2. Glucose 6-phosphate is converted into a 5-carbon ring isomer, fructose 6-phosphate.

3. Fructose 6-phosphate is phosphorylated by another ATP to form fructose 1, 6-diphosphate.

4. Fructose 1, 6-diphosphate is processed by an enzyme into two glyceraldehyde 3-phosphate

.

5. Two molecules of glyceraldehyde 3-phosphate are oxidized, losing hydrogen atoms and

gaining phosphate groups to form 1, 3-diphosphoglycerate. Two molecules of NAD+are

converted into NADH2+ in the process.

6. Two 1,3-diphosphoglycerate molecules phosphorylate ADP (adenine diphosphate) to yield

two molecules of3-phosphoglycerate and two ATPs are produced.7. The phosphate groups on 3-phosphoglycerate move to the 2nd carbon, forming2-

phosphoglycerate.

8. The two 2-phosphoglycerate molecules are dehydrated and forms two high-energy

phosphoenolpyruvate molecules.

9. The two phospoenolpyruvate phosphorylates two ADPs and produces two more ATPs and two

molecules ofpyruvate.


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Citric acid cycle or Kreb s cycle This is also called the Krebs cycle or the tricarboxylic acid cycle. When oxygen is

present, acetyl-CoA is produced from the pyruvate molecules created from

glycolysis. Once acetyl-CoA is formed, two processes can occur, aerobic or

anaerobic respiration. When oxygen is present, the mitochondria will undergo

aerobic respiration which leads to the Krebs cycle. However, if oxygen is not

present, fermentation of the pyruvate molecule will occur. In the presence ofoxygen, when acetyl-CoA is produced, the molecule then enters the citric acid cycle

(Krebs cycle) inside the mitochondrial matrix, and gets oxidized to CO2 while at the

same time reducin NAD to NADH. NADH can be used b the electron trans or

chain to create further ATP as part of oxidative phosphorylation. To fully oxidize theequivalent of one glucose molecule, two acetyl-CoA must be metabolized by the

Krebs cycle. Two waste products, H2O and CO2, are created during this cycle.

The citric acid cycle is an 8-step process involving different enzymes and co-

enzymes. Throughout the entire cycle, acetyl-CoA(2 carbons) + Oxaloacetate(4

carbons). Citrate(6 carbons) is rearranged to a more reactive form called

Isocitrate(6 carbons). Isocitrate(6 carbons) modifies to become -Ketoglutarate(5

carbons), Succinyl-CoA, Succinate, Fumarate, Malate, and finally, Oxaloacetate.


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Citric acid cycle

Krebs cycle


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Kreb s cycleAerobic Respiration

The pyruvate produced in glycolysis undergoes further breakdown through a process called aerobic respiration in most

organisms. This process requires oxygen and yields much more energy than glycolysis. Aerobic respiration is divided

into two processes: the Krebs cycle, and the Electron Transport Chain, which produces ATP through chemiosmotic

phosphorylation.

Krebs Cycle

The pyruvate molecules produced during glycolysis contain a lot of energy in the bonds between their molecules. In order

to use that energy, the cell must convert it into the form of ATP. To do so, pyruvate molecules are processed through

the Kreb Cycle, also known as the citric acid cycle.

1. Prior to entering the Krebs Cycle, pyruvate must be converted into acetyl CoA (pronounced: acetyl coenzyme A). This is

achieved by removing a CO2 molecule from pyruvate and then removing an electron to reduce an NAD+ into NADH. An

enzyme called coenzyme A is combined with the remaining acetyl to make acetyl CoA which is then fed into the Krebs

.

2. Citrate is formed when the acetyl group from acetyl CoA combines with oxaloacetate from the previous Krebs cycle..3. Citrate is converted into its isomer isocitrate..

4. Isocitrate is oxidized to form the 5-carbon -ketoglutarate. This step releases one molecule of CO2 and reduces NAD+ to

NADH2+.

5. The -ketoglutarate is oxidized to succinyl CoA, yielding CO2 and NADH2+.

6. Succinyl CoA releases coenzyme A and phosphorylates ADP into ATP.

7. Succinate is oxidized to fumarate, converting FAD to FADH2.

8. Fumarate is hydrolized to form malate.

9. Malate is oxidized to oxaloacetate, reducing NAD+ to NADH2+.

We are now back at the beginning of the Krebs Cycle. Because glycolysis produces two pyruvate molecules from one

glucose, each glucose is processes through the kreb cycle twice.


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metabolism 2

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