Non-Ruminant Protein Digestion

ANS 4190 Unit 1

(T or F) It only takes some of the 20 amino acids to build proteins.

False, it takes all 20

Chains of AAs are linked by ______ bonds.

Peptide

Protein digestion occurs to a limited extent in the ________.

Stomach

majority of hydrolysis and absorption of proteins occurs in the ________.

Small intestine

What is the purpose of HCl in the stomach? (2)

HCl uncoils the protein by breaking H bonds. It also activates Pepsin.

Inactive precursor form of a digestive enzyme

zymogen

Pepsin functions as peptidase at a pH <_____

3.5 (acidic)

Acidic chyme from the stomach enters the duodenum and causes the release of regulatory peptides and hormones. What two hormones are released? what do they do?

Secretin and cholecystokinin. They stimulate the pancreas to secrete pancreatic juice which contains bicarb and proteases. Enteropeptidase is also secreted from BB in response to CCK and secretin.

What 3 proteases are released by the pancreas?

Trypsinogen, chymotrypsinogen, and procarboxypeptidases A and B

Trypsinogen is activated into trypsin by….

enteropeptidase

Chymotrypsinogen is activated into chymotrypsin by….

trypsin (also chymotrypsin)

Procarboxypeptidase A and B is activated into carboxypeptidases by…

Trypsin

________ and _______ hydrolyze peptide bonds adjacent to amino acids

Trypsin and chymotrypsin

_______________ are zinc dependent.

Carboxypeptidases

Describe Na-coupled transport of AAs

Sodium binds to the amino acid transporter. This increases the affinity of AAs for the carrier. This binding forms a co-transporter. The transporter follows the Na gradient into the cytosol. The Na gradient is maintained by the Na+/K+ pump.

What major peptide transport protein helps peptides get into the enterocyte?

PEPT1

How does PEPT1 help peptides get into the enterocyte?

Peptides are coupled to a H+ and are transported into the cell. H+ is pumped back out in exchange for Na to maintain the sodium gradient. Now that the peptides are in the enterocyte they can be further digested.

(T or F) Most amino acids are absorbed as peptides

True

While peptides can enter the enterocyte via PEPT1, only _______ can exit. They use transporters to leave.

Free Amino Acids

(T or F) Most amino acids absorbed into enterocytes don’t leave. They are used to meet the protein needs of the cell.

True

Amino acids are catabolized (broken down) into two parts, what are they?

Amino group + carbon skeleton

What happens to the amino group after it is removed from the carbon skeleton?

It is either turned into urea or ammonia

What are the 3 ways a carbon skeleton from an amino acid can be used?

Energy and CO2, or glucos and ketone bodies, or fatty acids

Primary site of amino acid metabolism

Liver

_______ is the breakdown of AA

_______ is building AAs

Catabolism, anabolism

Skeletal muscle has a preference from catabolism of ___________ amino acids

branched chain

transfer of an amino group

transamination

removal of amino group

deamination

Detoxification/disposal of nitrogen

Formation of urea

What happens during a transamination reaction?

The amino group is removed from an AA and is transferred to an alpha-keto acid (carbon skeleton)

Why does transamination occur?

To make dispensable AA’s

Transamination is catalyzed by _______ which is dependent on _________

Aminotransferase, vitamin B6

Deamination reactions are the ______ of an AA group with no ________

removal, transfer

What happens to the amino acid carbon?

It can be further metabolized to produce energy, glucose, ketone bodies, and fatty acids

What enzyme is important in the urea cycle?

Carbonyl phosphate synthetase 1

The urea cycle functions in the ______ to remove ______ from the body

liver, ammonia

The liver contains _____ (all/some/none) of the enzymes of the urea cycle. The kidney contains all of the enzymes except _______.

all, arginase

Urea is excreted in the _____

Urine

During the 2 mitochondrial steps of the urea cycle, what comes in and what goes out?

NH4 and HCO3 are going in and carbamoyl phosphate is coming out

___________ is the rate limiting enzyme in urea synthesis

Carbamoyl phosphate synthetase 1

During the cytosolic steps of the urea cycle _______ goes in and _________ and ________ come out

NH3, urea, ornithine

Tissue protein synthesis is stimulated by __________. It causes amino acid transporters to move to the cell membrane. It also inhibits some enzymes responsible for AA degradation.

insulin

Cell organelles that degrade proteins

Lysosomes

_________ degradation of proteins _______ require energy.

Lysosomal, doesn’t

Lysosomes contain a variety of digestive enzymes that are only active at an acidic pH which is achieved by a ______ ________.

Proton pump

_________ is a large structure with a central cavity for degradation of proteins. The majority of proteolysis occurs in __________. This type of degradation is responsible for the degradation of abnormal, damaged, or denatured proteins.

Proteasome, skeletal muscle

Describe ubiquination

A damaged protein will be tagged with ubiquitin which requires energy. This helps the proteasome find the damaged protein and turn it into a free amino acids

The urea cycle functions in the liver to remove ________ from the body.

Ammonia

Deamination is dependent on what vitamin?

Vitamin B6

Which of the following processes involved in protein metabolism does not likely require energy?

a. Absorption of most amino acids

b. Lysosomal protein degradation

c. Proteosomal protein degradation

d. Urea cycle

lysosomal protein degradation (b)