Glucose-1

The value of ∆G° corresponds to…

the crude indication of the likelihood of a reaction

The value of ∆G corresponds to…

the true (in vivo) indication of the likelihood of a reaction

Negative ∆G°

Endergonic = requires energy

Positive ∆G°

Exergonic = produces energy

∆G=0

Reversible reaction

∆G<0

Irreversible + produces energy

Glucose uptake in the GIT happens through which mechanisms?

Active and Passive transport

Where does Active transport happen?

Intestinal villi

Example of Active transport

Na+/Glc symport

What allows the Na+/Glc symport to happen?

The Na+/K+ pump maintains a low internal Na+ concentration

Where does Passive transport happen?

In other cell types (muscles)

Example of passive transport

Glc enters cells passively (down the concentration gradient)

When does the pancreas come into play after a meal?

When the plasma Glc concentration exceeds 5.5mM

How does the pancreas come into play after a meal?

Pancreatic beta cells release insulin upon membrane depolarization

Why does membrane depolarization happens?

After glycolysis, the K_ATP channel opens through ATP production

How does insulin help with glucose uptake?

It stimulates Glc uptake via transporters

Which tissues share the GLUT4 transporter?

Adipose tissue and muscle

Which organ is NOT insulin responsive?

Liver

Why are there so many different GLUTs? (3)

1. Tissue specificity

2. Level of expression

3. Sugar specificity

What are liver cells called?

Hepatocytes

In what form is Glc stored in the fed state?

Glycogen

What enzyme is used to drive the formation of glycogen?

Synthase

What enzyme is used to break down the glycogen in the fasting state?

Phosphorylase

What is the next pathway the liver uses during the fasting state?

Gluconeogenesis

What is different about the way the muscle stores glycogen?

It is not stored as abundantly as in the liver

3 pathways used by the muscle during exercise

1. Use G6P

2. Break down glycogen

3. Import Glc from blood

How do fat cells (adipose) behave in the fed state?

It transforms Glc into triglycerides

How do fat cells behave in the fasting state/while exercising?

They supply fatty acids

How do the other tissues (Kidney, brain, etc) use Glc?

Through aerobic glycolysis of circulating blood sugar (NO STORAGE)

What energy source is used in the first 6 seconds of running?

ATP stored in the muscles

What energy source is used in the next 10 seconds?

ATP formed from creatine phosphate + ADP through creatine kinase

What pathway is used in the next 40 seconds?

Anaerobic glycolysis

What pathway is used in long term exercise?

Aerobic lipolysis

What are the 3 steps of ATP generation?

1. Glycolysis

2. Citric acid cycle

3. Ox. phosphorylation

What are the outcomes of glycolysis?

Glc → 2 ATP + 2 NADH + 2 pyruvates

What are the outcomes of the CAC?

Acetyl-CoA → NADH + FADH₂

What are the outcomes of ox. phosphorylation?

NADH+FADH₂+O₂ → ATP

What is specific about pyruvate?

It is at the crossroads of many processes

Specificity of glycolysis

The only process that doesnt require oxygen

What are the 2 processes that do not require O₂?

Homolactic and alcoholic fermentation

What enzymes are involved in the rate determinant steps?

1. Hexokinase

2. Phosphofructokinase (PFK)

3. Pyruvate kinase (PK)

What is hexokinase’s job in the cell?

Once phosphorylated:

1.Trap G-6-P in cell

2.Create a gradient

Why do liver cells use both hexokinase and glucokinase?

The extra Glc is converted into glycogen by glucokinase