Ch.10 Carb Metabolism Flashcards
Where does starch digestion start? What enzyme is found in saliva?
Starts in the mouth; enzyme α-amylase
What happens when food enters the small intestine?
Mixes with pancreatic juice, which contains more α-amylase.
What 3 oligosaccharides are formed after entering the small intestine?
maltose, maltotriose, alpha-dextrin
What is the last step of starch digestion?
convert maltose, maltotriose, and alpha-dextrin into glucose
What two enzymes play a role in oligosaccharide conversion to glucose during starch digestion?
maltase and α-dextrinase
Where are maltase and α-dextrinase located?
Microvilli (Tiny finger-like structures that line the small intestine)
What 2 disaccharides do our diets consist of?
sucrose (sweet foods) and lactose (milk)
What enzymes break down disaccharides? What do they breakdown to?
Sucrase and lactase; glucose, fructose, galactose
What is absorbed into the cells lining the small intestine after digestion?
monosaccharides (simple sugars)
What helps moves sugars into the cells?
transport proteins
What is the completing step to carbohydrate absorption?
monosaccharides exit cells, enter bloodstream, making sugars available for bodily use
Where do sugars in the bloodstream travel to?
Liver –> acts as a distribution center for carbs
How does the liver store sugar?
Stores some as glycogen, releases the rest to bloodstream
List characteristics of the liver
- manages carbs
- turns sugar into glycogen
- glycogen typically amounts to 3-7% of overall weight
List characteristics of muscles
- store glycogen for energy
- glycogen amounts to 1-1.5% of overall muscle weight
Which contains more glycogen in the body?
Liver has higher percentage of glycogen, but muscles store more glycogen overall
Where is glycogen found?
cytosol of liver/muscle cells; forms tiny granules in the cells
What is glycogenesis?
builds glycogen for energy storage; adds glucose molecules together making long chains
Where does energy come from to make glycogen?
ATP and UTP (uridine triphosphate)
First step of glycogenesis
Turn ATP into glucose 1-phosphate
Second step of glycogenesis
Mix glucose 1-phosphate with ATP to create UDP-glucose
What enzyme helps add glucose molecules to glycogen chain?
Glycogen synthase
What happens to UDP when glucose is added?
UDP is released, ready to be used again in later formations of UDP-glucose, allowing further glycogen synthesis
What is the starting point for glycogen synthase? What protein makes this up?
primer made up of glycogenin
What is glycogenin’s role?
adds 8 glucose molecules to itself, then glycogen synthase adds more glucose to the chain
What makes glycogen a branched chain?
branching enzyme (moves parts of chain inside the glycogen molecule to form branches)
What is glycogenolysis?
Breaking down of glycogen into glucose 1-phosphate and plain glucose
What bonds are breaking during glycogenolysis? What causes the breaking?
glycosidic linkages broken through phosphorolysis (Pi helps break bonds)
What is created through breaking of glycosidic linkages? What enzyme causes this?
glucose 1-phosphate; glycogen phosphorylase
What is phosphorylase’s role?
goes through glycogen and removes glucose until it’s 4 glucose residues away from a branch point
What happens when the chain becomes really short?
Debranching enzyme helps phosphorylase
What 2 jobs does the debranching enzyme have?
- moves 3 of the 4 glucose residues from a branch to the end of another branch
- breaks bond at the branch point, leaving plain glucose
Both glycogenesis and glycogenolysis are ________. Meaning what?
Anaerobic processes; occur without the need for oxygen
What speeds up glycogenolysis in the muscles?
Exercise/ physical activity
What 4 factors speed up glycogenolysis?
- Pi concentration increase
- Ratio of AMP to ATP
- Calcium ion concentration
- Hormonal control
How does the increase of Pi concentration contribute to speeding up glycogenolysis?
It contributes to the conditions that favor phosphorylase activation.
As AMP levels ____ (while ATP levels ____), it activates ________, facilitating glycogenesis.
rise, decrease, phosphorylase b
While AMP binding activates Phosphorylase b, this activation is only _______.
temporary
The phosphorylation of phosphorylase b (to form a) is a more ______ and longer-lasting activation mechanism.
stable
