Non-Aerobic Carbohydrate Metabolism Flashcards
the breakdown of complex molecules in living organisms to form simpler ones, together with the release of energy; destructive metabolism.
catabolism
the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy; constructive metabolism.
anabolism
What are the two basic pathways that glucose is used to provide energy?
- substrate level phosphorylation
- oxidative phosphorylation
Process in which a phosphate group of a substrate is transfered to ADP to make ATP during glycolysis
takes place in the cytoplasm during glycolysis and in the mitochondria during Kreb’s cycle
the addition of phosphate groups is called
phosphorylation
the process of forming ATP via the transfer of electrons in the ETC
What is the name of this process?
oxidative phosphorylation
What are the two oxidizing agents used in oxidative phosphorylation?
NADH
FADH2
Remember: these two oxidizing agents are also coenzymes
The role of reduced NAD and FAD is to provide electrons for the electron transport chain. In the Kreb’s cycle, they are reduced to NADH and FADH2. The extra hydrogen ions in these coenzymes dissassociate and are actively transported across the inner mitochondrial membrane. The electrons are donated to the first and second electron carrier proteins in the electron transport chain. These electrons move down the transport chain, losing free energy as they move. It is this energy that is used to actively transport the hydrogen ions across the inner mitochondrial membrane!
What are two ways in which sugar can enter the bloodstream?
- Absorption from small intestine and liver cells
- Cells in the renal cortex produce it via gluconeogenesis or glycogenolysis
What family of receptors help glucose diffuse through the plasma membrane?
GLUT family
Why can’t glucose diffuse through the cell membrane by itself
Glucose is too polar, thus it must use GLUT receptors to transport it across the plasma membrane
Name the glucose transport receptor
expressed throughoutbody and is responsible for constant low-level baseline glucose intake
GLUT1
expressed by liver, pancreatic beta, and some kidney cells. It is a bidirectional transporter that allows glucose to be transported both in and out of the cell. Crucial for gluconeogenesis
GLUT2
primarily expressed in neurons and placenta. High-affinity transporter (can transport glucose even when blood glucose levels are low).
GLUT3
expressed in skeltetal and cardiac muscle and adipose tssues. Regulated by insulin. Main role is to store glucose in skeleta, cardiac, and adipose tissues when there is surplus glucose levels in blood. Implicated in type 2 diabetes
GLUT4
the initial metabolic pathway in the metabolism of carbohydrates that can occur with or without oxygen
glycolysis
Glycolysis is the major pathway of glucose metabolism and occurs in the cytosol of all cells. It can occur aerobically or anaerobically depending on whether oxygen is available. This is clinically significant because oxidation of glucose under aerobic conditions results in 32 mol of ATP per mol of glucose. However, under anaerobic conditions, only 2 mol of ATP can be produced
Familiarity video
In-depth video
expresed in skeletal and cardiac muscle, and adipose tissues. Regulatied by insulin. Main job is storing glucose
GLUT4
where does glycolysis take place?
the cytosol
What are the major outcomes of glycolysis?
- glucose is broken down to produce 2 molecules of pyruvate
- NAD+ gets converted to NADH
- ATP production
serves as a means of energy production in cells that cannot produce adequate energy through oxidative phosphorylation. In poorly oxygenated tissue, this process produces 2 ATP by shunting pyruvate away from mitochondria and through the lactate dehydrogenase reaction
anaerobic glycolysis
What are the products of anaeorobic glycolysis?
2 ATP + lactic acid (animals) or ethanol (yeast)
Why does fermentation occur in anaerobic glycolysis?
NADH needs to be converted to NAD+ for glycolysis to continue, but in the abscence of oxygen, fermentation provides a way for NAD+ to be regenerated
Describe ethanol fermentation
This is used by yeast and consists of 2 steps:
1. Pyruvate loses a carboxylic acid functional group, becoming an acetalaldehyde and carbon dioxide (this step is catylyzed by pyruvate decarboxylase)
2. Alcohol dehydrogenase turns acetaladehyde into an ethanol in a reaction coupled to the conversion of NADH to NAD+
Describe the steps in lactic acid fermentation
Pyruvate is converted to lactate by lactate dehydrogenase in a reaction used to convert NADH to NAD+. This process takes place in human muscle cells.
Where does gluconeogenesis occur?
The liver (50-60%), kidneys (40%) and to some extent in the adrenal cortex and intestines
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the liver regulates blood glucose levels so ensuring an adequate glucose supply is throughout the body’s tissues
List the ways in which glycolysis is different from gluconeogenesis
- The main difference between gycolysis and gluconeogenesis is that glycolysis is involved in the glucose catabolism whereas gluconeogenesis is involved in the glucose anabolism.
- Gluconeogenesis STARTS with pyruvate
- The final step of glycolysis is skipped by gluconeogenesis
- Early stages of glycolysis where phosphate groups are added are bypassed
What is the purpose of gluconeogenesis?
To provide a ready source of glucose to the body - particularly for liver cells use - when blood glucose levels are low
Why are the early stages of glycolysis where the phosphate groups are added bypassed in gluconeogenesis?
Because 1.) they are irreversible and 2.) involves ATP investment. It would not make sense for gluconeogenesis to reverse these steps bc doing so would mean creating ATP, which is the job of ATP synthase in the ETC. Instead, gluconeogenesis bypasses these steps by catylyzing a hydrolysis reactrion, splitting off a Pi from the carbohydrate
Why is the final stage of glycolysis bypassed in gluconeogenesis?
1.) it is irreversible
2.) The cell must avoid a futile cycle in which pyruvate from glycolysis is immiediately converted back to PEP. This is why gluconeogenesis has a two-step pathway split up between the mitochondria and the cytoplasm
Fill in the blank
Each glycogen molecule is formed around a core formed by the protein ____, which is the base for glycogen synthesis. This protein also helps catylyze the buildup of the first 8 glucose molecules, after which glycogen synthase can take over
Glycogenin
Fill in the blanks
Glycogen molecules are linked together by ____ within each branch, while ____ linkages form seperate branches
Glycogen molecules are linked together by 𝝰(1–>4) within each branch, while 𝜶(1–>6) linkages form seperate branches
The synthesis of glycogen
Glycogenesis
Name the metabolic pathway
Process where glucose is shunted off from glycolysis/gluconeogenesis pathway and ‘marked’ for [insert process here] by moving the phosphate group
Glycogenesis
Name the enzyme
During glycogenesis, this enzyme forms the 𝝰(1–>4) linkages between molecules of glucose to form the growing glycogen strand. It does this by catalyses the incorporation of uridine diphosphate-glucose (UDP-glucose) into glycogen in skeletal muscle
glycogen synthase
Name the enzyme
Forms new branches of 𝜶(1–>6) linkages
glycogen-branching enzyme
Name the metabolic pathway
The biochemical pathway in which glycogen breaks down into glucose-1-phosphate and glucose. The reaction takes place in the hepatocytes and the myocytes. The process is under the regulation of two key enzymes: phosphorylase kinase and glycogen phosphorylase.
glycogenolysis
Name the enzyme (fill in the blank)
Glycogen phorylase, like ____ , only works on ⍺(1–>4) linkages
Glycogen synthase
What two enzymes deal with α(1–>6) linkages in glycogen metabolic pathways?
- Glycogen branching enzyme and
- glycogen debranching enzyme
Name the metabolic process
Shunts glucose-6-phosphate away from glycolysis/gluconeogenesis pathway and uses it to do other structurally important things. Particularly, it converts NADP+ to NADPH and converts glucose-6-phosphate into ribose 5-phosphate
This product serves the functions of a.) being a reducing agent needed to synthezize lipids and nucleic acids and b.) helps protect against damage from reactive oxygen synthesis by regenerating the antioxidant glutathione from its oxidative form
NADPH
Name the phase and the pathway
Oxidizes a glucose 6-phosphate into a ribose 6-phosphate while in the process generated two NADPH molecules, a carbon dioxide and 2 H+ ions.
Oxidative phase of the pentose-phosphate pathway
Name the phase and the pathway
Links the glycolytic pathway to the ____ pathway and it allows our cells a way to break down ribose molecules ingested into our body. This phase uses several important enzymes, including phosphopentose isomerase, phosphopentose epimerase, transketolase and transaldolase.
Non-oxidative phase of the pentose phosphate pathway
Glycolyisis is upregulalted when ____ and downregulated when ____
Glycolyisis is upregulalted when the cell needs more ATP, and downregulated when the cell does not need more ATP
Describe how negative regulation is used in glycolysis
Certain products inhibit previous steps in glycolysis. I.e, when glucose-6-phospahte (the first product of glycolysis) inhibits hexokinase, which catalyzes the conversion of glucose to glucose-6-phosphate
When is gluconeogenesis upregulated?
there are 2 answers
**When the body needs more glucose **AND as an alternate pathway to hadndle surplus pyruvate/acetyl-CoA that builds up
True or False
Gluconeogenesis and glycolysis are regulated in tandem to respond to hormonal signaling from outside the body
True
Most notably, the signaling is from insulin and glucagon
When does the body break down glycogen?
What is the purpose of glycogen breakdown
When cells need more glucose for gluconeogenesis or glycolysis
Remember: glycogen is how the cells store excess glucose
When is glycogen synthesis upregulated?
When the cells have a surplus of glucose
thus needing this glucose to be stored (as glycogen) for later use
When there are surplus levels of AMP/ADP, which non-aerobic metabolic pathways are affected and how?
Glycolysis is upregulated because the cell needs energy
AMP rises whenever the ATP:ADP ratio falls, and a high cellular ratio of AMP:ATP is a signal that the energy status of the cell is compromised.
When there are high levels of ATP/NADH/citrate, which non-aerobic metabolic pathways are affected and how?
Glycolysis is downregulated because the cell has enough energy
When there is excess acetyl-CoA, what non-aerobic metabolic pathway is affected and how?
Gluconeogenesis is upregulated because acetyl-CoA activates pyruvate carboxylase, which converts pyruvate to oxaloacetate (OAA) for use in the gluconeogenic pathway
Inhibition of pyruvate dehydrogenase by acetyl-CoA also increases shunting of pyruvate toward oxaloacetate.
How does the presence of glucagon influence the metabolic pathways?
It upregulates gluconeogenesis and downregulates glycolysis
Glucagon acutely stimulates hepatic gluconeogenesis by increasing hepatic acetyl-CoA content and pyruvate carboxylase flux.
How does the presence of glucagon affect glycoysis?
Glucagon downregulates glycolysis, whereas insulin upregulates glyclolysis
To increase blood glucose, glucagon promotes hepatic glucose output by increasing glycogenolysis and gluconeogenesis and by decreasing glycogenesis and glycolysis in a concerted fashion via multiple mechanisms.
How does insulin affect gluconeogenesis and glycolysis?
Insulin downregulates gluconeogenesis and upregulates insulin
Insulin indirectly stimulates glucose oxidation via increasing glucose uptake and subsequent glycolysis that increases pyruvate supply for mitochondrial glucose oxidation by the pyruvate dehydrogenase (PDH) complex, the rate-limiting enzyme of glucose oxidation. Insulin is the most important hormone that inhibits gluconeogenesis. It acts predominantly by suppressing the expression of the genes for the key gluconeogenic enzymes PEPCK and G-6-Pase.
