Chapter 2: Bioenergetics and Carbohydrate Metabolism

Midterm Part II

Bioenergetics

• the study of energy changes accompanying biochemical reactions in biological systems

• field of biochemistry concerned with the transformation and use of energy by living cells

Catabolic Reactions

• involve the breakdown of chemical molecules

Anabolic Reactions

• involve the synthesis of compounds

Adenosine Triphosphate (ATP)

• the main energy currency for organisms

synthesize ATP and break down ATP

The goal of metabolic and catabolic processes are:

1. to _____________ from available starting materials

   1. to _____________ into (ADP and Pi) by utilizing it in biological process

Free Energy

• the energy actually available to do work (utilizable) is known as __________

Changes in Free Energy

• are valuable in predicting the feasibility of chemical reactions

• the reactions can occur spontaneously if they are accompanied decrease in free energy

• during a chemical reaction, heat may be released or absorbed

Photosynthetic cells

• acquire free energy from absorbed solar radiation

Heterotrophic cells

• acquire free energy from nutrient molecules

First law of thermodynamics

• principle of conservation of energy

• for any physical/chemical change, the total amount of energy in closed system remains constant

First Law of Thermodynamics

• energy cannot be created or destroyed - it can only be changed from one form to another

Second law of thermodynamics

• universe tends toward increasing disorder

• in all natural processes, the entropy of the universe increases (unless energy requiring processes counteract it)

Gibbs free energy (G)

• which is equal to the total amount of energy capable of doing work during a process at constant temperature and pressure

Exergonic

• if G is negative, then the process is spontaneous and termed ________

Endergonic

• if G is positive then the process is non spontaneous and termed __________

Equilibrium

• if G is equal to zero then the process has reached __________

Enthalpy (H)

• the total heat energy in a system

• the amount of heat energy transferred (absorbed/emitted) in a chemical process under constant pressure

Exothermic

• when H is negative, the process produces heat and is termed ______

Endothermic

• when H is positive, the process absorbs heat and is termed __________

Entropy (S)

• quantitative expression of the degree of randomness or disorder of the system

• measures the amount of heat dispersed or transferred during a chemical process

Increased

• when S is positive, then the disorder of the system has _________

Decreased

• when S is negative, then the disorder of the system has ________

G = H - T(S)

Relationship between the change in Free energy, Enthalpy and Entropy

Exergonic Reaction

• implies the release of energy from a spontaneous chemical reaction without any concomitant utilization of energy

• these reactions have an ability to perform work and include most of the catabolic reactions in cellular respiration

Exergonic Reaction

• most of these reactions involve breaking of bonds during the formation of reaction intermediates

Endergonic Reaction

• most anabolic reactions like photosynthesis and DNA and protein synthesis are ______ in nature

Endergonic Reaction

• non-spontaneous reaction, energy should be provided from outside for the progression of the reaction

Nutrition

• the science of how the body utilizes food to meet requirements for development, growth, repair and maintenance

Carbohydrate

• most abundant organic molecule on earth

• all carbohydrates have the general formula

• are defined as aldehyde or keto derivatives of polyhydric alcohols

Aldose

Ketose

Triose

Classification of Carbohydrates by Number of Carbons:

What is the generic name for the carbohydrates with 3 carbons?

Tetrose

Classification of Carbohydrates by Number of Carbons:

What is the generic name for the carbohydrates with 4 carbons?

Pentose

Classification of Carbohydrates by Number of Carbons:

What is the generic name for the carbohydrates with 5 carbons?

Hexose

Classification of Carbohydrates by Number of Carbons:

What is the generic name for the carbohydrates with 6 carbons?

Monosaccharides

• the smallest, most basic units of carbohydrates

Monosaccharides

Properties:

• sweet-tasting

• quickly absorbed

• soluble in water

Disaccharides

• made of two monosaccharides joined together

Disaccharides

Properties

• still sweet

• need to be broken down into monosaccharides before absorption

Oligosaccharides

• made up of a few (typically 3-10) monosaccharide units linked together

Oligosccharides

Properties:

• usually not very sweet

• often partially/poorly digested by humans

Raffinose

Components:

Galactose + Glucose + Fructose

Stachyose

Components:

2 Galactose + Glucose + Fructose

Fructooligosaccharides (FOS)

Components:

• Short chains of fructose

Galactooligisaccharides

Components:

• chains of galactose

Raffinose

Found:

• beans

• cabbage

• broccoli

Stachyose

Found:

• soybeans

• legumes

Fructooligosaccharides

Found:

• onions

• garlic

• bananas

• chicory

Galactooligosaccharides

Found:

• human milk

• legumes

Raffinose

Notes:

• can cause gas

Stachyose

Notes:

• harder to digest

Fructooligosaccharides

Notes:

• prebiotic

Galactooligosaccharides

Notes:

• also prebiotic

Polysaccharides

• long chains of monosaccharides

Fischer Formula/Fischer Projection

• is a two-dimensional way of representing the 3d structure of organic molecules, especially sugars and amino acids

Penultimate Carbons

• Carbon atom that determines if a sugar is D or L

• the chiral carbon farthest from the aldehyde or ketone functional group (2nd to the last C)

Haworth Projection Formula

• cyclic structures of sugars

• method used to show the 3d stereochemistry of cyclic sugars (or saccharides)

Anomers

• differ only in the configuration at the hemiacetal carbon

a-OH

• is pointing down

b-OH

• is pointing up

Isomers

• compounds that have the same chemical formula but have different structures

Epimers

• are carbohydrates that differ in the location of the -OH group in one location

Energy Source

Functions of Carbohydrate:

• main fuel for cells (especially brain & red blood cells)

Sparing Protein

Functions of Carbohydrate:

• prevents protein breakdown for energy

fat metabolism

Functions of Carbohydrate:

• needed for complete fat metabolism; otherwise, ketones form

Digestive Health

Functions of Carbohydrate:

• fiber supports bowel health & regularity

Brain Function

Functions of Carbohydrate:

• brain relies heavily on glucose (about 120g/day)

Metabolism

• is the set of chemical reactions that occur in living organisms to maintain life

Convert food into energy, build and repair tissues, eliminate waste products and support all bodily functions

Metabolism allows the body to (4):

Catabolism

• breaks down larger molecules into smaller ones

• releases energy

• ends with “lysis”/”oxidation”

Anabolism

• builds up complex molecules from simpler ones

• uses energy

• ends with “genesis”/”synthesis”

Glucose in the bloodstream

• after you eat carbohydrates, your body breaks them down into glucose which enters the bloodstream

Insulin release (in most cases)

• the pancreas releases insulin (a hormone)

• some tissues require insulin for glucose uptake, while others dont

Glucose Transporters (GLUT proteins)

• these are membrane proteins that facilitate glucose entry into cells

Glucose entry via GLUT4 (muscle and fat)

• in insulin-sensitive tissues like muscle and adipose (fat):

  • insulin binds to insulin receptors on the cell membrane

  • GLUT4 transporters are moved to the cell membrane

  • glucose enters the cell through GLUT4

  • once inside, glucose can be:

    • used for energy (via glycolysis)

    • stored as glycogen (in muscle/liver), or;

    • converted into fat (in adipose tissue)

Glycolysis

• Embden-Meyerhof-Parnas Pathway / E.M.P. Pathway

• is the metabolic pathway that breaks down one molecule of glucose (6-carbon) into two molecules of pyruvate (3-carbon), producing small amounts of energy in the form of ATP and NADH

Citric Acid Cycle/ Kreb’s Cycle/ Tricarboxylic Acid/TCA Cycle

• is a central metabolic pathway that:

  • takes place in the mitochondrial matrix

  • requires oxygen indirectly (aerobic conditions)

• converts Acetyl-CoA into Co2, while producing high-energy electron carriers (NADH, FADH2) and ATP

Gluconeogenesis

• is the metabolic process by which the body creates glucose from non-carbohydrate sources - mainly during fasting, starvation, or intense exercise

Lactate

Major Precursors:

• from anaerobic glycolysis

Alanine (Amino Acids)

Major Precursors:

• from protein breakdown

Glycerol

Major Precursors:

• from fat breakdown (triglycerides)

Propionate

Major Precursors:

• from odd-chain fatty acids (minors)

Glycogenesis

• anabolic process of synthesizing glycogen from glucose

• store excess glucose as glycogen for later use