Metabolism

Question 1

What is the conversion of glycogen to glucose called

Answer 1

glycogenolysis

Question 2

From glucose to three carbon chain (pyruvate)?

Answer 2

Glycolysis

Question 3

From 3-C chain (pyruvate) to glucose?

Answer 3

gluconeogenesis

Question 4

From glucose to glycogen?

Answer 4

Glycogenesis

Question 5

Fatty acids are stored as?

Answer 5

triglycerides

Question 6

Triglycerides can be broken down into?

Answer 6

fatty acids and glygerol

Question 7

What do we get when we break down a fatty acid?

Answer 7

An acetyl Co-A (2 C chain) that can enter the citric acid cycle

Question 8

A two carbon chain also be made into what (instead of entering the citric acid cycle)?

Answer 8

Fatty acid synthesis begins with acetyl-Co A. Because acetyl-Co A is the common intermediary for all aerobic catabolic pathways, fatty acids can be synthesized from excess carbohydrates or amino acids.

Question 9

What is the primary use of amino acids in the body?

Answer 9

Synthesis of proteins. These are rarely used if other energy sources are available, only in starvation.

Question 10

Which events occur at the mitochondria?

Answer 10

The citric acid cycle, which produces Coenzymes for the electron transport chain, also in the mitochondria. This process is aerobic (consuming oxygen and producing carbon dioxide).

Question 11

In one sentence, what does the citric acid cycle do?

Answer 11

It transfers hydrogen atoms to coenzymes.

Question 12

What feeds into the citric acid cycle?

Answer 12

Pyruvate. It gets cleaved into acetate, which gets converted into acetyl-CoA. Acetyl-CoA is what directly enters the citric acid cycle. We generate Coenzymes with Hydrogens that are ready to be fed into the electron transport chain.

Question 13

Describe the events of the electron transport chain.

Answer 13

Coenzymes. 2 molecules of NADH or 1 molecule of FADH2. The hydrogen atoms are delivered to Coenzyme Q, which releases the H+’s but keeps the electrons to feed them into the cytochrome line up. Oxygen accepts the low energy electrons and with hydrogen ions, forms water. The entire purpose here is to create a concentration gradient of protons on the inter membrane space. When hydrogens flow down their gradient into the mitochondrial space, they power an ATP synthase.

Question 14

Where are the cytochromes physically located?

Answer 14

Embedded in the inner membrane space of the mitochondrion.

Question 15

What is the preferred substrate for catabolism and ATP production under resting conditions?

Answer 15

Carbohydrates

Question 16

What are the first steps in the breakdown of carbohydrates?

Answer 16

Salivary amylase breaks down complex carbohydrates into di and trisaccharides. This form of amylase breaks down by the time it hits the stomach acid. When chyme arrives at the duodenum, secretin stimulates the release of buffers that shift the pH up. CCK gets released and this triggers the secretion of pancreatic enzymes, including pancreatic alpha-amylase, which is not as wimpy.

Question 17

What happens to the disaccharides in the chyme as they enter the duodenum/jejunum?

Answer 17

They trigger the release of GIP, which stimulates insulin release by the pancreas. The cells at the jejunum finish the digestion of carbs. Those cells utilize the enzymes maltase, sucrase, and lactase to convert the disaccharides into monosaccharides. The sugars then diffuse into the capillaries for transport to the liver.

Question 18

What happens when the simple sugars reach the liver?

Answer 18

They are absorbed here and if needed, converted into glucose. The glucose is released into the blood to maintain normal glucose levels of about 90. Excess is stored as glycogen or used in other ways.

Question 19

How does glucose enter cells for catabolism?

Answer 19

It requires a carrier protein which must be stimulated by insulin. Inside the cell, the glucose can be converted into ribose, if needed. For energy, it is broken down into pyruvate through glycolysis.

Question 20

What is the first step of glucose metabolism in the cell?

Answer 20

Glycolysis.

Question 21

Describe glycolysis.

Answer 21

We start with 6 carbon glucose. It gets split in the process. We generate some coenzymes along the way. Glycolysis uses energy to make energy, but at the end of glycolysis proper, we net 2 ATP. However, after the products from glycolysis go through the citric acid cycle and oxidative phosphorylation, the we net 36 ATP per glucose molecule.

Question 22

In one sentence, how do lipids reach the bloodstream?

Answer 22

Lipid reach the bloodstream in chylomicrons; the cholesterol is then extracted and released as lipoproteins

Question 23

What are the very first steps in digesting lipids?

Answer 23

Our saliva contains lingual lipase. This breaks triglycerides into monoglycerides and fatty acids. Sadly, the mixing of chyme in the stomach creates large drops containing a variety of lipids. Lipase can only act on the surface of the drops. Only 20% get broken down by the time we leave the stomach.

Question 24

How does fat get processed at the level of the duodenum?

Answer 24

When chyme reaches the duodenum, CCK is released, triggering the secretion of pancreatic enzymes, including pancreatic lipase and stimulation gallbladder contraction and ejection of bile into the duodenum. Now bile salts from the bile break the large lipid drops into tiny droplets (emulsification). Pancreatic lipase can now more effectively break apart the triglycerides to form a mixture of fatty acids, monoglycerides, and glycerol. They form little lipid bile salt complexes called micelles.

Question 25

What happens when a micelle contacts the intestinal epithelium?

Answer 25

They diffuse across the plasma membrane and enter the cytosol. Here we do something weird by making new triglycerides from the monoglycerides and fatty acids and glycerol. These triglycerides along with cholesterol, phosphlipids, etc, get coated with proteins making complexes known as chylomicrons. The protein makes it water soluble and then the intestinal cells secrete these into interstitial fluid by exocytosis. But they are too big to get into the capillaries!

Question 26

What happens to chylomicrons in the interstitial fluid?

Answer 26

Most of them diffuse into the intestinal lacteals of the lymphatic system, which lack basement membranes. From here, the chylomicrons proceed into the thoracic duct and enter the bloodstream at the left subclavian vein then pass through the pulmonary circuit then systemic circuit. Capillary walls have a lipoprotein lipase so that the fatty acids and monoglycerides can diffuse into the interstitial fluid. Now they can be used by the muscles for energy or absorbed by adipocytes.

Question 27

What happens to chylomicrons at the liver?

Answer 27

They get absorbed and the liver turns them into LDL’s and VLDL’s. The VLDL’s transport tryglycerides from the liver to muscle and adipose tissue, while the LDL’s enter the blood stream to go to peripheral tissues, where they can be absorbed into cells.

Question 28

What do cells do with LDL’s?

Answer 28

They bring them in and fuse them with a lysosome to release the cholesterol, which it uses in synthesis of membrane or hormones, etc. The unused cholesterol diffuses out of the cell across the PM and reenters the bloodstream. Here HDL’s (proteins released by the liver) absorb excess cholesterol and transport it back tot he liver to be used for bile or for storage.

Question 29

Briefly describe the absorptive state of metabolic activity

Answer 29

About four hours following a meal, when nutrients are absorbed. Here, insulin is king.

Question 30

Briefly describe the post absorptive state

Answer 30

WE rely on energy reserves to maintain blood glucose levels. Various hormones are involved.

Question 31

In the absorptive state, what happens specifically?

Answer 31

insulin stimulates glucose uptake and glygogenesis. Insulin also stimulates aa uptake and protein synthesis, and triglyceride synthesis.

Androgens, estrogens, and GH also stimulate protein synthesis.

Glycolysis and aerobic metabolism provide the ATP needed to power cellular activities as well as the synthesis of lipids and proteins.

Question 32

In the post absorptive state, what happens specifically?

Answer 32

Glucocorticoids stimulate the mobilization of lipid and protein reserves; these effects are enhanced by GH.

Glucagon stimulates glycogenolysis and gluconeogenesis, primarily in the liver. The release of glucose by the liver and the shift away from glucose metabolism by other tissues stabilizes blood glucose levels.

Epinephrine is important in stimulating glycogenolysis in skeletal and cardiac muscle, and lipolysis in adipocytes.