PROTEIN-Part OneNFSC 303 – Nutrition and Fitness

McCafferty

FUNCTIONS

structure for tissues

transporters:

fluid balance

acid/base balance

Basic Unit: Amino Acid

N essential from dietBasic structure:

C

R group varies --

It takes 20 Amino Acids to make most proteins

Essential AAs tryptophan valine threonine isoleucine leucine lysine phyenylalanine methionine histidine

Nonessential AAs alanine arginine asparagine aspartic acid cysteine glutamic acid glutamine glycine proline serine tyrosine

A Few Terms:Conditionally Essential AA:

Transamination:

Deamination:

Building Proteins from AAs

Polypeptide = several to hundreds of AAs linked together

Quaternary Structure: 2 or more polypeptides associated with each other, e.g. hemoglobin

Protein Digestion & Absorption

Mouth:

Stomach:

Sight/smell/thought of food plus

entry of food into the stomach

stimulate ____________________.

HCl

Small Intestine

AAs

(absorbed)

AAs are absorbed into the blood

AAs circulate through the liver

Any AAs that aren’t used to synthesize body proteins are “wasted.”

Deaminated:

Remaining C skeletons are:

Using Protein to Make ATP

What is protein made of?

What are the functions of protein?

Do we store protein?

Remember

Each AA contains N, and must be deaminated before entering these pathways

Once the N is removed, 2-C and 3-C units remain, about half and half (simple story)

Amino Acids Amino Acids

C SkeletonsC Skeletons

( )( )

Glucose 6CGlucose 6C

Pyruvate 3CPyruvate 3C

Acetyl CoA 2CAcetyl CoA 2C

KrebsKrebsETSETS

The 2C units enter at The 3C units enter at

We don’t store protein the same way we store CHO (glycogen) or fat (adipose) Excess protein intake:

•

•

Summary of ATP Production from Protein

Under normal diet and exercise conditions, protein is not an important ENERGY source

Amino acids must be deaminated before they can be metabolized

Complete oxidation of AA’s produces urea, ATP, H2O and CO2.

Summary of ATP Production from Protein

Because of their 3C skeleton, about half the carbons from AA’s (protein) can be used to synthesize glucose

Excess dietary protein is not stored as protein, but rather is used to produce ATP or is stored as fat (adipose)

GLUCONEOGENESIS

The Making of New Glucose

Remember:

Exogenous fuels: from outside the body dietary protein, CHO, and fat

Endogenous Fuels: from within the body glucose from glycogen fatty acidsfatty acids from adipose amino acids from body proteins

• importance increases in times of inadequate kcalories or CHO intake

Remember...Every cell uses glucoseSome cells are glucose dependent

Gluconeogenesis is the making of new glucose form 3-carbon compounds

Gluconeogenic compounds: pyruvate lactate glycerolglycerol 3C AA’s, particularly alanine

Body Protein as a Source of Glucose

To supply glucose to glu-dependent tissues, body proteins are catabolized

Body Protein as a Source of Glucose

Remember, TG is catabolized too, but much more slowly, since only the glycerol (3C)glycerol (3C) can be used to synthesize glucose

So after the first 24 hours of a fast:

Ketone Bodies: An Alternative Fuel to Glucose?

Ketone Bodies: An Alternative Fuel to Glucose?

KBs are carried to other tissues for ATP production

LiverLiver

Non-liver TissuesNon-liver TissuesAdipose & Lean Adipose & Lean Body TissuesBody Tissues

Acetyl CoAAcetyl CoA

Ketone BodiesKetone Bodies

Ketone BodiesKetone Bodies

Acetyl CoAAcetyl CoA

Krebs (ATP)Krebs (ATP)