basic concepts of metabolism

digestion is the process in which ____ is converted into molecules that can be used for ____ and/or _____ → it prepares ____ for entry into _____

• food

• energy

• building blocks

• large molecules

• metabolic pathways

food must be degraded into ____ for absorption by epithelial cells of the ____ and for transport in __ __ → food needs to be homogenized to an ___ ___

• small molecules

• intestine

• the blood

• aqueous slurry

proteins are digested to __1__ by ___2__ secreted by the __3__ & __3__

polysaccharides are cleaved into __4__ by __5__ from the __6__ & __6__ (to a lesser extent)

lipids are converted into __7___ by __8___ secreted by the __9___

1. amino acids

2. proteolytic enzymes (proteases)

3. stomach & pancreas

4. monosaccharides

5. ⍺-amylase

6. pancreas & saliva

7. fatty acids

8. lipases

9. pancreas

what are zymogens (2) + give 2 examples

• proenzymes that are inactive but activated by proteolytic cleavage

• they exist in granules near the cell membrane + fuse w membrane expelling their contents into lumen of intestine

  • ie. trypsinogen → trypsin

  • pepsinogen → pepsin

trypsinogen is cleaved by _____ at the ____ and turned into ____

• enteropeptidase

• N-terminus

• trypsin

all of the zymogens + their active proteases

1. trypsinogen —enteropeptidase→ trypsin

2. proelastase → elastase

3. procaboxy-peptidase → carboxy-peptidase

4. chymotrypsinogen → chymotrypsin

5. prolipase → lipase

saliva contains ___ which cleaves the ______ glycosidic bonds & also contains ____ which cleaves ____ in TAGs

• amylase

• ⍺-1,4 glycosidic bonds

• lipase

• ester bonds

after the food passes into the stomach, what 2 activities take place? (2)

1. proteins are denatured by the acidic environment of the stomach (pH ~1-2)

2. pepsin begins protein degradation

what two things does the pancreas secrete?

1. pancreatic proteases to hydrolyze proteins into oligopeptides

2. sodium bicarbonate (NaHCO3) which neutralizes the pH of the stomach as food exits the stomach

the denaturation of proteins in the stomach is caused by ___

caused by the breakage of ionic + hydrogen bonds due to the low pH

where + by whom is digestion of proteins completed (2)

• completed by peptidases attached to the external surfaces of the intestinal cells

• cleave the oligopeptides → amino acids + di-/tripeptides that can be transported into intestinal cells by transporters

starch is primarily digested by the enzyme ___ found in the _____ which cleaves ____ bonds but not the ____ and yields three end products

1. ⍺-amylase

2. pancreas

3. ⍺-1,4 bonds

4. ⍺-1,6 bonds

5. yields:

   1. maltose

   2. maltotriose

   3. ⍺-limit dextrin

enzymes that digest the di-/trisaccharide products of starch (3) + where are they present

present on the surfaces of the intestinal cells

1. ⍺-glucosidase digests maltotriose

2. maltose —maltase→ glucose

3. ⍺-dextrinase digests limi dextrin

digestion of disaccharides + where do the enzymes reside (3)

reside on the surfaces of intestinal cells

1. sucrose —sucrase→ glucose + fructose

2. lactose —lactase→ glucose + galactose

triacyglycerols are degraded to ____ + ____ by enzymes secreted by the pancreas called ____

1. free fatty acids

2. monoacylglycerol

3. lipases

once activated, lipases attach to the ____ + cleave off two of the _____

• lipid droplets

• fatty acids

free fatty acids form ____ + are carried to the plasma membrane of the ______ where they will be _____

1. micelles

2. intestinal epithelial cells

3. absorbed

what is metabolism (2)

• a series of linked chemical reactions

• begins with a particular biomolecule and converts it into some other required biomolecule

catabolism vs anabolism

• catabolism: transform fuel into cellular energy

  • glucose + 6O2 → 6H2O + 6CO2 + ATP

• anabolism: use energy to build complex molecules

  • amino acid + cellular energy → proteins

what does it mean that it has a high phosphoryl transfer potential? (3)

• it has a high phosphoryl transfer potential = tendency of a molecule to transfer its phosphoryl group to an acceptor molecule

• large amount of free energy liberated when ATP is hydrolyzed to ADP + Pi

• ATP has greater phosphoryl transfer potential than G3P AKA stronger tendency of ATP to turn terminal phosphoryl group into water

  

why is it important that ATP is an intermediate among the biologically important phosphorylated molecules?

• intermediate position allows ATP to function efficiently as a carrier of phosphoryl groups

what four factors differentiate the stability of the reactants (ATP) and products (ADP + Pi)

1. electrostatic repulsion of the 4 charges of ATP reduced when ATP hydrolyzed

2. Pi has greater resonance stabilization than phosphates in ATP

3. the entropy of the products is greater bc now there are two molecules

4. H2O binds + stabilizes ADP + Pi to a greater degree making the reverse rxn aka synthesis of ATP less favorable

The ATP/ADP cycle (4)

• 100 g of ATP in body → resting human burns 40 kg/day

• V. high ATP turnover

• short-term energy storage molecule

• ATP is constantly used + regenerated

oxidation vs reduction

• oxidation: loss of electrons

• reduction: gain of electrons

• redox rxn = coupled oxidation-reduction

what are activated carriers in metabolism + what do they carry + vitamin precursor

• small molecules carrying an activated functional group that can be transferred to acceptor molecules

  • NADH/NADPH: carry electrons → vitamin B3

    

  • FADH2: carry electrons → vitamin B2

    

  • coenzyme A: acyl → vitamin B5 → carrier of 2-carbon fragments