Proteins are large, complex, organic molecules made up of **amino acids**.
	- Contain carbon, hydrogen, oxygen, and nitrogen
	- Found in plants, animals, bacteria, and viruses
- Major functions of protein in the body:
	- To build new cells and many parts of cells
	- As a component in hardened structures like hair and nails
	- As enzymes to speed chemical reactions
	- As lubricants to ease movement
	- In clotting compounds in blood
	- To build antibodies that fight disease organisms
	- As compounds that help maintain fluid and pH balance
	- As transporters
	- To make certain hormones
	- As an energy source (as a last resort)
# Introduction
- By helping to maintain fluid balance, proteins prevent **edema** (accumulation of fluid in tissues
- Proteins also help maintain **acid-base balance**.
	- Maintaining the proper pH of body fluids
	- Acts as a buffer

# Amino acids
- Amino acids are nitrogen containing chemical units that comprise proteins
- There are 20 different amino acids found in the proteins of the human body
- Each amino acid has a carbon atom that anchors
	- Hydrogen atom
	- Amino or nitrogen containing group
	- R group (side chain)
	- carboxylic acid group
- nonessential amino acids are a group of amino acids that the body can make
- Essential amino acids are amino acids the body cannot make or cannot make enough of to meet its needs
- Conditionally essential amino acids are the amino acids the body cannot make or cannot make enough of to meet its needs
- There are 9 essential acids and 11 non-essential acids

| Essential                    | Nonessential  |
| ---------------------------- | ------------- |
| Histidine                    | Alanine       |
| Isoleucine                   | Aspartic acid |
| Leucine                      | Asparagine    |
| Lysine                       | Glutanic acid |
| Methionine                   | Serine        |
| Phenylanaline                | Argine        |
| Threonine                    | Cysteine      |
| Tryptophan (extra important) | GLutamine     |
| Valine                       | Glycine       |
|                              | Proline       |
|                              | Tyrosine      |
TT HILL MVP

# Synthesis
A specific order of amino acids is needed to formulate a protein. 

# DNA
- DNA (deoxyribonucleic acid) provides instructions for making proteins.
	- **Genes** are a portion of DNA
	- To make proteins, cells assemble amino acids into specific sequences according to information from DNA
- A **peptide bond** is a chemical attraction that connects two amino acids together

# DNA Process
1. Protein synthesis begins when a section of DNA unwinds, exposing a single portion (a gene). The gene contains coded info about the order of amino acids that comprise a specific protein
2. The gene undergoes **transcription**, that is, the sequence of amino acids copied is copied in a special manner, forming **messenger  RNA** (mRNA) in the process.
3. mRNA transforms the information concerning the amino acid sequence form the nucleus to **ribosomes**, protein manufacturing sites in cytoplasm.
4. During the **translation** process, ribosomes "read" mRNA. The coded instructions indicate which amino acid to add to the polypeptide chain and its sequence.
5. Each specific **transfer RNA** (tRNA) molecule conveys a particular amino acid to the ribosome.
6. At the ribosome, the amino acid that has been delivered by the tRNA attaches to the peptide chain, lengthening it. 
7. When the translation process is complete, the ribosome release the polypeptide, and the new protein generally undergoes further processing at other sites within the cytoplasm.

Summary:
- Transcription: DNA unwinds, gene gets copied forming mRNA, happens in the nucleus
	- DNA -> mRNA
- Translation: mRNA give info to ribosomes and they "read" mRNA. trNA gets each amino acid and brings it to the ribosome to be attached to the peptide chain. Happens in **cytoplasm**.
	- mRNA -> ribosomes, ribosomes read mRNA -> tRNA grabs the amino acid needed -> ribosomes create peptide chain

# Protein Structure
- The shape of protein is important because it influences the compound's function
- Sickle cell anemia is an inherited form of anemia.
- **Denaturation** alters a protein's natural shape and function by exposing it to conditions such as heat, acids, and physical agitation. This change is permanent. 

# In Foods
- Animal foods generally provide higher amounts of protein than similar quantities of plant foods.
- Certain parts of plants provide more protein than other parts
	- Seeds, tree nuts, legumes supply more
	- Fruits or edible leaves, roots, flowers, and stems of vegetables provide less
- Legumes are parts of plants that produce pods with a single row of seeds.
	- Peas
	- Peanuts
	- Lentils
	- Soybeans
- High quality (complete) protein is a protein that contains all essential amino acids in amounts that support the deposition of protein in tissues and the growth of a young person.
	- Meat, fish, poultry, eggs, **milk**
- Low quality (incomplete) protein is a protein that lacks or has inadequate amounts of one or more of the essential amino acids
- A limiting amino acid is the essential amino acid found in the lowest concentration of a particular protein source\

- A healthy adult's RDA for protein is **0.8 g/kg** (apparently low)
- Protein needs increase during
	- Pregnancy
	- Breastfeeding
	- Periods of rapid growth
	- Recovery
		- Serious illness
		- Blood losses
		- Burns

# Digestion
- Protein digestion begins in the stomach
- Hydrochloric acid denatures food proteins and activates pepsin
	- Gastric enzymes that break proteins down into smaller polypeptides
- After polypeptides enter the small intestine, the pancreas secretes protein splitting enzymes.
- Trypsin and chymotrypsin
- Enzymes released by absorptive cells break down shortened peptides into dipeptides and tripeptides
	- Two and three amino acids respectively
- Amino acids are carried to absorptive cells by carrier systems
- After absorption, amino acids enter the capillary of villus
	- Travel to liver via hepatic portal vein
	- Liver keeps some amino acids
		- Release the rest into circulation
- Protein turnover is the cellular process of breaking down proteins and recycling their amino acids.
	- Endogenous is a source of nitrogen from within the body
	- Exogenous is a source of nitrogen from outside the body
		- Dietary protein
- **Deamination** is the removal of nitrogen-containing group from an amino acid.
- A carbon skeleton is the remains of an animo acid following deanimation and removal of the nitrogen containing component of the amino acid. Can be used to create glucose, energy, or fatty acids.
- Transamination is the transfer of the nitrogen containing group from an unneeded amino acid to a carbon skeleton to form an amino acid.
- Blood urea nitrogen (BUN) is a measure of the concentration of urea in blood.
	- Assesses kidney function
	- Normal values are from 7-20 mg/dL
- Urine urea nitrogen (UUN) is a measure of the concentration of 

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