Chapter 10 Study Guide

lecture portion

All chemical reactions and physical workings of the cell

Metabolism

Anabolism: Biosynthesis:

synthesis of cell molecules and structures

· Requires energy input

Catabolism

Break the bonds of larger molecules

° Releases energy

Speed up the rate of a chemical reaction without becoming part of the products or being consumed in the reaction

Catalysts

Enzymes overcome the activation energy allowing the reaction to proceed by:

Increasing thermal energy to increase the velocity of molecules

o Increasing the concentration of reactants to increase the rate of molecular collisions

· Adding a catalyst

Enzyme Characteristics

Composed of protein; may require cofactors

Lower the activation energy required for a chemical reaction to proceed

Have unique characteristics such as shape, specificity, and function

Enable metabolic reactions to proceed at a speed compatible with life

Have an active site for target molecules (substrates)

Are not used up or permanently changed by the reaction

Can be recycled

Are greatly affected by temperature and pH

Can be regulated by feedback and genetic mechanisms

Substrates:

reactant molecules upon which enzymes act

Enzymes bind to substrates and participate directly in

changes to the substrate

note: Does not become part of the products, Is not used up by the reaction, Can function over and over again

METALLIC COFACTORS consist of

Iron, copper, magnesium, manganese, zinc, cobalt, selenium,etc.

ICMMZCS

METALLIC COFACTORS Assist with

precise functions between enzyme and substrate

· Activate enzymes

. Help bring the active site and substrate close together

. Participate directly in chemical reactions

COENZYMES

Organic compounds that work with the apoenzyme to alter the substrate

COENZYMES do what

Remove a chemical group from one substrate and add it to another substrate

Carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups

Vitamins are an important component of coenzymes

Simple enzymes: consist of

protein alone

Conjugated enzymes (holoenzyme): contain

protein and some other nonprotein molecule

Apoenzyme

protein portion of the enzyme

Cofactor

nonprotein portion; organic or inorganic (metal ions)

Coenzyme

organic cofactors

Oxidoreductases:

transfer electrons from one substrate to another, and dehydrogenases transfer a hydrogen from one compound to another

Transferases:

transfer functional groups from one substrate to another

cleave bonds on molecules with the addition of water

Hydrolases

Lyases:

add groups to or remove groups from double-bonded substrates

Isomerases:

change a substrate to its isomeric form

catalyze the formation of bonds with the input of ATP and the removal of water

ligases

Exoenzymes:

· Transported extracellularly

· Break down large food molecules or harmful chemicals

Retained intracellularly and function there

· Most enzymes of metabolic pathways

Endoenzymes

Always present in relatively constant amounts, regardless of the cellular environment

Constitutive enzymes

Regulated enzymes

Production is turned on (induced) or turned off (repressed) in response to changes in concentration of substrate

Role of Microbial Enzymes in Disease:

Pathogens secrete unique exoenzymes that help them avoid host defenses or promote multiplication in tissues

Considered virulence factors or toxins because they contribute to disease

EXAMPLES:

· Streptokinase- digests blood clots

· Elastase & collagenase- digest elastin and collagen

Weak bonds that maintain the shape of an apoenzyme are broken by heat, low or high pH, or certain chemicals

Denaturation

Disruption causes distortion of

the enzyme's shape.

Prevents the substrate from attaching to the active site

Nonfunctional enzymes block ______ and can lead to cell death

metabolic reactions

Competitive inhibition:

A molecule that resembles the substrate occupies the active site, preventing the substrate from binding

Enzyme cannot act on the inhibitor and is effectively shut down

Non competitive inhibition

Some enzymes have two binding sites-the active site and the regulatory site

Regulated by the binding of molecules other than the substrate to the regulatory site

Non competitive inhibition: Often, the ______ ______ is the product of the enzymatic reaction

regulatory molecule

Provides negative feedback that slows enzyme activity once a certain concentration of product is reached

Controls on Enzyme Synthesis: 2 terms

repression and inudction

REPRESSION

Stops further synthesis of an enzyme somewhere along its pathway

If the end product of an enzymatic reaction reaches excess, the genetic apparatus for replacing enzymes is repressed

Response time is longer than for feedback inhibition, effects more enduring

INDUCTION

Enzymes appear (are induced) only when suitable substrates are present

Synthesis of an enzyme is induced by its substrate

Inverse of enzyme repression

release energy as they go forward

· Energy is available for doing cellular work

Exergonic reactions

Endergonic reactions:

. Require the addition of energy to move forward

· Exergonic and endergonic reactions are often coupled

ATP aka Adenosine Triphosphate

3 part molecule

Adenine: nitrogen base

Ribose: 5 carbon sugar

In ATP, 3 phosphate groups bonded to the ribose

They’re bulky and have a NEGATIVE charge

Repelling electrostatic charges imposes a strain between the last 2 phosphate groups

Removal of phosphates releases free energy

Metabolic Role of ATP:

Primary energy currency of the cell

When it is used in a chemical reaction, it must be replaced

ATP utilization and replenishment is an ongoing cycle

generation of ATP through a transfer of a phosphate group from a phosphorylated compound directly to ADP

Substrate-level phosphorylation

-a series of redox reactions occurring during the final phase of the respiratory pathway

Oxidative phosphorylation

Photophosphorylation

ATP formed through a series of sunlight-driven reactions in phototrophs

3 basic catabolic pathways

aerobic respiration

anaerobic respiration

fermentation

_____ is the most common pathway used to break down glucose

glycolysis

AEROBIC RESPIRATION

Series of reactions that converts glucose to CO2 and allows the cell to

recover significant amounts of energy

Glycolysis

The Krebs cycle

Respiratory chain

Utilizes glycolysis

the Krebs cycle and the respiratory chain but does not use molecular oxygen as the final electron acceptor

Final electron acceptor: NO-3

ANAEROBIC RESPIRATION

Fermentation Pathway

Facultative and aerotolerant anaerobes

Uses only glycolysis

Oxygen is not required; use organic compounds as electron acceptor

Nitrite and Nitrate Reduction Systems

Nitrate reductase catalyzes the reaction of nitrate to nitrite and water

Testing for this is one major physiological tests of bacteria ID

The Four Stages of Cellular Respiration

Glycolysis

Preparatory Reaction

The Citric Acid Cycle

Electron Transport Chain

Glycolysis

· Breakdown of glucose into pyruvate, 2 ATP

Preparatory Reaction

. Pyruvate is oxidized- CO2 and NADH formed

The Citric Acid Cycle

· 2 ATP produced

Electron Transport Chain

. H20 created, 32 ATP generated

in eukaryotes, glycolysis occurs in the

cytoplasam

. Glucose (6 carbons) broken down into

two molecules of pyruvate (3 carbons)

. Divided into:

. Energy-investment steps

. Energy-harvesting steps

Energy-investment step

· 2 ATP transfer their phosphates to glucose

Energy-harvesting step

. Substrate-level ATP synthesis produces 4 ATP

. Net gain of 2 ATP

. 2 NADH made

Krebs cycle

also known as the citric acid cycle,

a series of chemical reactions that extract energy from molecules like acetyl-CoA. It's a crucial part of cellular respiration, occurring in the mitochondria of cells.

The cycle converts acetyl-CoA into carbon dioxide, releasing energy that's captured in molecules like NADH, FADH2, and ATP.

The incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

Uses organic compounds as the terminal electron acceptors

Yields a small amount of ATP

What is this process called?

Fermentation

Occurs in yeast or bacterial species that have metabolic pathways for converting pyruvic acid to ethanol

alcohol fermentation

products of alcoholic fermentation

Decarboxylation of pyruvic acid to acetaldehyde

Reduction of acetaldehyde to ethanol

NADH formed during glycolysis is oxidized, regenerating NAD and allowing glycolysis to continue

In alcoholic fermentation, pathways are

extremely varied

Homolactic fermentation:

Lactic acid bacteria reduce pyruvate to lactic acid only

Heterolactic fermentation:

glucose is fermented to a mixture of lactic acid, acetic acid, and carbon dioxide

Lipases break apart and fatty acids are

joined to glycerol

Glycerol converted to dihydroxyacetone phosphate which can enter step 4 of glycolysis

Beta oxidation:

Oxidation of fatty acids

2-carbon units transferred to coenzyme A, creating acetyl CoA, which

enters the Krebs cycle

Oxidation of a 6-carbon fatty acid yields 50 ATP, compared to 38 for a 6-

carbon sugar

Protein catabolism: Proteases break down

Break down proteins to their amino acid components.

Amino groups removed through deamination

Remaining carbon compound can be easily converted to one of several

Krebs cycle intermediates

Amphibolism:

° Most catabolic pathways contain strategic molecular intermediates that can

be diverted into anabolic pathways

A given molecule can serve multiple purposes to derive

maximum benefit from all nutrients and metabolites.

_____ and ____pathways are integrated to improve cell efficiency

Catabolic and anabolic

cellular building blocks (2)

pyruvate, acetyl CoA

Pyruvate is a precursor, it provides

Provides intermediates for amino acids

Gluconeogenesis (gluco-neo-genesis)

pyruvate is starting point for glucose synthesis in the event of inadequate glucose supply

Acetyl CoA is a precursor:

. Can be converted into one of several amino acids

. Can be condensed into hydrocarbon chains for fatty acid and lipid synthesis

Precursors to DNA and RNA:

. Pathways that synthesize purines and pyrimidines originate in amino acids

· Can be dependent on intermediates from the Krebs cycle

During times of carbohydrate deprivation, organisms can convert amino acids to

intermediates of the Krebs cycle and derive energy from proteins

Carbohydrate Biosynthesis:

Crucial role of glucose in metabolism/energy utilization:

. ensured by several alternative pathways

. Major component of cellulose cell walls and storage granules

· Glucose-6-P used to form glycogen

Protein Synthesis

· Large proportion of a cell's constituents

° Essential components of enzymes, cytoplasmic membrane, cell wall, and cell appendages

o 20 amino acids are needed to make these proteins

Cell division: (process)

· Two cells need twice as many ribosomes, enzymes, etc.

o Cell wall and membranes nearly double

o Phospholipid bilayer components assemble spontaneously with no energy input

o Proteins and other components must be added to the membranes

o Cell wall growth requires energy input

______ ______photosynthesis

· Chlorophyll needed

. ATP is produced

Light Dependent photosynthesis

Light Independent photosynthesis

. "Calvin Cycle"

· Energy from ATP reduces CO2

The main events of the light reaction shown as an exploded view in one granum.

1.When light activates photosystem II, it sets up a chain reaction, in which electrons are released from chlorophyll.

2.These electrons are transported along a chain of carriers to photosystem I.

3.The empty position in photosystem II is replenished by photolysis of H2O. Other products of photolysis are O2 and H+.

4.Pumping of H+ into the interior of the granum produces conditions for ATP to be synthesized.

5.The final electron and H+ acceptor is NADP, which receives these from photosystem I.

6.Both NADPH and ATP are fed into the stroma for the Calvin cycle.

Oxygenic (oxygen-releasing) photosynthesis:

. Dominant type on earth

. Occurs in plants, algae, and cyanobacteria

Anoxygenic photosynthesis:

· Occurs in green and purple bacteria that utilize bacteriochlorophyll

· Have only cyclic photosystem I

. Generate a small amount of ATP

· Use H2, H2S, or elemental sulfur as an electron source

. Many are strict anaerobes