Proteins and Amino Acids:Function Follows Form

BIOL 103, Chapter 7-1

Today’s Topics

• Why is Protein Important?• Amino Acids are building blocks of proteins• Functions of Body Proteins• Protein Digestion and Absorption• Proteins in the Body

Why is Protein Important?

• A part of every cell• Needed in thousands of chemical reactions• Keep us “together” structurally• In short, proteins have many, many functions

from replacing skin cells, producing antibodies to assisting in nutrient transport and muscle contractions.

Food Sources of Proteins

• Beef• Chicken• Fish• Milk• Plant foods: beans, peas,

grains, nuts, seeds, and vegetables (garlic, green peas, mushrooms)

Amino Acids are Building Blocks of Proteins

• Proteins are sequences of amino acids• There are _____ amino acids:

1. _______________________ (9)2. _______________________ (11)3. _______________________ (6)• Amino acids that are normally dispensable, but

become indispensable under certain circumstances such as during critical illness.

• Table 7.1 List of Amino Acids

Amino Acids Identified by Side Chains

• Identified by side chains – Made up of: _____________________________– _____________ gives AA its identity

Protein structure: unique 3D shapes and functions

• Amino Acid Sequence– Amino acids are linked by ______________:• Dipeptide: ____ amino acids• Oligopeptide: _____amino acids• Polypeptide: _____ amino acids• Protein: ___________________________________

– Protein shape• A sequence of AA determines protein _____________• Shape of protein determines its __________________

Protein Denaturalization: Destabilizing a Protein’s Shape

• There are factors that can cause a protein to unfold and lose shape (denature)1. Changes in Acidic or Alkalinity in

environment2. _____________________3. Alcohol4. _____________________

• Denatured proteins lose _____ _________________________– e.g. egg protein, avidin

Functions of Body Protein

1. ___________________________________– _______________: fibrous protein found in bones,

teeth, connective tissue, blood vessel structure.– _______________: water-soluble fibrous proteins

found in hair, nails, and outer layer of skin.– _______________: proteins that use energy and

convert it to mechanical work (e.g. muscle contraction, cell division, sperm movement)

2. ___________________________________– _______________: infection-fighting protein

molecules that tag, neutralize, and help destroy bacteria/viruses or toxins.

Functions of Body Proteins

3. ________________• Catalyze (speed up) chemical reactions

4. ________________– “chemical messengers”– Regulate ______________

5. ________________– Proteins as _____________________ by picking up H+

or donate H+• Too acidic/low pH: Acidosis• Too basic/high pH: Alkalosis

Functions of Body Proteins

6. _____________________– ____________________ (e.g. active transport)– ____________________ (e.g. lipoproteins)

7. ____________________________– Fluids inside (intracellular), between (interstital),

and outside (intravascular) of body cells must be balanced.

– If diet lacks proteins ___________________ ____________________ _______________

Functions of Body Proteins

8. __________________________________– Although your body prefers using fat and

carbohydrates, if necessary, your body will break down protein ___________________

– Protein can be broken down for energy: ________________________________• Removes nitrogen from amino acids so that only

carbon skeleton is left.

Protein Digestion

• Protein digestion– Cells produce proteases (protein-digesting

enzymes) as proenzymes (inactive forms of enzymes)

– In the stomach:• Proteins are denatured by ____________• Pepsin begins digestion: _____________ of proteins• Which one is a protease? A proenzyme?

Protein Digestion and Absorption

• In the small intestine: – ____________ (from pancreas) break down

remaining proteins _______________– ________________ break down small peptides

_________________________– Amino acids are then absorbed into your

_________________ travel via portal vein to ___________________ released to _____________________

Undigested Proteins

• If not digested, continues down the GI tract _________________

• Diseases of the intestinal tract cause problems with digestion/absorption of proteins1. Celiac disease: _________________________2. Cystic fibrosis: ______________ prevents

digestive enzymes (e.g. proteases) from reaching small intestine __________________ nutrients are not absorbed malnutrition

Proteins in the Body

• Protein Synthesis:– Draws on AA pool as needed. If your body is

missing…• Non-essential AA:

• Essential AA:

Proteins in the Body

• Amino Acid Pool and Protein Turnover– Cells in your body constantly build and breakdown

proteins ______________________________• ____________________: because we are always

recycling our proteins, we need so little protein in our diet!

– When cells make proteins, they use amino acids from ______________________ : available amino acids in body tissues and fluids that can be used to make new proteins.

Proteins in the Body

• Synthesis of nonprotein molecules– Proteins are precursors of ___________________

______________

• Protein and Nitrogen Excretion– Breakdown of amino acids by removing ________

_ ________________– Amino groups converted to ___________– Urea + water = _________ excretion (in kidney)

Nitrogen Balance• We can evaluate our nitrogen balance to evaluate what is

happening in our body– Nitrogen intake vs. nitrogen output

• Nitrogen equilibrium– Nitrogen intake _____ nitrogen output– ______________________________________

• Positive nitrogen balance– Nitrogen intake _____ Nitrogen output– ______________________________________

• Negative nitrogen balance– Nitrogen intake _____ Nitrogen output– ______________________________________