Chapter 12: Metabolism and Bioenergetics

Flashcards covering key concepts and details from the lecture on Metabolism and Bioenergetics to assist in exam preparation.

What do cells break down or catalyze large molecules to release?

Free energy and small molecules.

What is the process called when cells rebuild larger molecules using free energy?

Anabolism.

What constitutes an organism's metabolism?

The set of all catabolic and anabolic activities.

What are chemoautotrophs?

Microorganisms that obtain metabolic materials and free energy from inorganic compounds (CO2, N2, H2, and S2)

What do photoautotrophs require for photosynthesis?

CO2, H2O, nitrogen, and sunlight.

How do heterotrophs obtain their building materials and energy?

From organic compounds produced by chemo- or photoautotrophs.

As heterotrophs, mammals rely on food produced by other organisms. After food is digested and absorbed, what happens?

It becomes a source of metabolic energy and materials to support the animal’s growth and other activities.

What are the four types of biological molecules in the human diet?

The macromolecular polymers known as: Proteins, nucleic acids, polysaccharides, and triacylglycerols.

What are the monomeric components resulting from the digestion of proteins, nucleic acids, polysaccharides, and triacylglycerols?

Amino acids, nucleotides, monosaccharides, and fatty acids.

Where does digestion take place in humans? Catalyzed by what?

In the mouth, stomach, and small intestine and is catalyzed by hydrolytic enzymes.

What role do lipases play in digestion?

It’s synthesized by the pancreas and secreted into the small intestine to catalyze the release of fatty acids from triacylglycerols.

What begins the breakdown of starch in the digestive process?

Salivary amylase. It consists of linear polymers of glucose residues (amylose) and branched polymers (amylopectin).

What are gastrin and pancreatic proteases responsible for?

Degrading proteins into small peptides and amino acids.

How do monosaccharides enter the cells lining the intestine?

Via active transporters such as the Na+-glucose system. Similar symport systems bring amino acids and di- and tripeptides into the cells.

What do triacylglycerol digestion products re-form inside the cell?

Triacylglycerols.

Some fatty acids are linked to cholesterol to form what?

Cholesteryl esters

What are lipoproteins specifically called when they are formed with triacylglycerols and cholesteryl esters? Where are they released?

Chylomicrons. They are released into the lymphatic circulation before entering the bloodstream for delivery to tissues.

What tissue specializes in the long-term storage of nutrients like fatty acids?

Adipose tissue.

What form do fatty acids take in adipocytes?

Intracellular fat globules.

What is glycogen?

The storage polymer of glucose.

What happens to glucose that does not become part of glycogen?

It can be catabolized to two-carbon acetyl units and converted to fatty acids for storage as triacylglycerols.

How are amino acids used in the body?

To build polypeptides and proteins. A protein is not a dedicated storage molecule for amino acids.

The excess amino acids can be broken down and converted to what?

Carbohydrate (which can be stored as glycogen) or converted to acetyl units (which can be converted to fat).

When are amino acids mobilized to generate energy?

During a fast when glycogen stores are depleted.

What is the degradation of glycogen called?

Phosphorolysis, this enzymatic process releases glucose 1-phosphate units from the glycogen polymer, catalyzed by glycogen phosphorylase.

What two major pathways degrade unneeded proteins?

Lysosomal breakdown and proteasome degradation.

What marks a protein for destruction by the proteasome?

Ubiquitin. A chain of atleast four ubiquitins is required to label the protein for degradation.

What are metabolic pathways?

Series of reactions for converting biopolymers to monomers and vice versa.

What is glycolysis?

The metabolic pathway that degrades glucose.

What is the two-carbon acetyl group linked to in acetyl-CoA?

Coenzyme A (CoA).

What is oxidation in metabolic terms?

The loss of electrons. (OIL)

What is reduction in metabolic terms?

The gain of electrons. (RIG)

What happens during the oxidation of carbon in metabolic reactions?

C—H bonds are replaced with C—O bonds.

What is the relationship between carbon oxidation and photosynthesis?

Photosynthesis reduces carbon dioxide to carbohydrate.

What are cofactors or coenzymes?

Organic compounds that allow enzymes to carry out particular reactions.

Ubiquinone can take up to how many electrons in contrast to NAD+?

Ubiquinone can accept up one or two electrons, while NAD+ strictly a two-electron carrier.

What can generate a considerable amounts of reduced cofactors?

Catabolic pathways, such as the citric acid cycle.

What is oxidative phosphorylation?

The process where reduced cofactors are reoxidized to produce ATP. In mammals, the reoxidation of NADH and QH2 and the concomitant production of ATP require the reduction of O2 to H2O.

How are macromolecules managed for energy in mammalian fuel metabolism?

Macromolecules are stored and then mobilized so that their monomeric units can be broken down into smaller intermediates. These intermediates are further degraded (oxidized) in metabolic pathways, and the released electrons are collected by cofactors (such as NAD+ and FAD) for subsequent use in ATP production.

What are the fundamental characteristics of metabolic pathways?

1. Interconnectedness: Pathways are not isolated; substrates of one pathway often serve as products for another, creating a complex network.

2. Regulation: Pathway activity is tightly controlled (regulated flux) based on factors like substrate availability and the cell's energetic needs (e.g., ATP levels). This regulation ensures polymers are not synthesized when monomers are scarce, nor are fuels catabolized unnecessarily.

3. Cellular Specificity: Not all cells carry out every metabolic pathway, meaning each cell possesses a unique metabolic repertoire.

4. Organismal Interdependence: Organisms can be metabolically interdependent, relying on each other for certain metabolic products or processes.

What is the role of the liver in nutrient processing?

To catabolize, store, or release nutrients into the bloodstream.

How do metabolic pathways interact in a cell?

They are interconnected; substrates of one pathway can be products of another.

What do humans lack that makes them reliant on other species for nutrition?

Many biosynthetic pathways and synthesis of essential amino acids and vitamins.

Why do humans need vitamins in their diet?

Because they cannot synthesize certain compounds necessary for health.

What vitamin deficiency causes beriberi?

Thiamine (Vitamin B1) deficiency.

What is Niacin, what coenzymes is it a part of, and what deficiency disease is associated with it?

A component of coenzymes NAD+ and NADP+, which are crucial for numerous metabolic redox reactions. Its deficiency causes pellagra, a disease characterized by symptoms such as diarrhea, dermatitis, and in severe cases, dementia. Humans can synthesize niacin from the essential amino acid tryptophan. Historically, pellagra was prevalent in populations whose diets were primarily based on untreated maize (corn), as maize is low in tryptophan and its niacin is covalently bound to other molecules, making it poorly absorbed. Traditional preparation methods, such as soaking maize kernels in an alkaline solution, release this bound niacin and prevent the deficiency.

What reaction involves ATP and drives other reactions forward?

ATP hydrolysis, which is highly exergonic.

What happens during unfavorable reactions when coupled with favorable reactions?

The net change in free energy is less than zero.

What is the standard free energy change for ATP hydrolysis?

Approximately -30 kJ/mol.

What is Gibb's Free Energy Change influenced by?

Reactant concentrations and equilibrium constant.

What can unfavorable reactions depend on to proceed?

Coupling with favorable reactions.

What method is used to calculate actual free energy changes?

Using concentrations of reactants in the mass action ratio.