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 environment 2._____________________ 3.Alcohol 4._____________________ 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 proteins 1.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 – ______________________________________