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Chapter 6: Proteins and Amino Acids

Published on Feb 03, 2016

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PRESENTATION OUTLINE

Chapter 6: Proteins and Amino Acids

Proteins

  • A class of nutrients that include molecules made up of one or more intertwining chains of amino acids
  • Contain carbon, hydrogen, oxygen, and nitrogen
Proteins (also sometimes called peptides)

Contain carbon, hydrogen, oxygen, and nitrogen (makes them chemically distinct from other macronutrients)

Large, complex molecules found in the cells of living things.

Protein size is variable, and depends on the number of amino acids present, which is why they are often classified on the basis of their number of amino acids
Photo by kevin dooley

Protein Structure

  • Made up of one or more intertwining chains of amino acids.
  • Peptide bonds: links amino acids together.
Photo by kevin dooley

How Proteins are Made: Peptide Bonds

  • Dipeptide: two amino acids linked together
  • Tripeptide: three amino acids linked together.
  • Oligopeptide: 4-9 amino acids linked together
  • Polypeptide: >10 amino acids linked together

Untitled Slide

  • The order and chemical properties of the amino acids in the polypeptides determine the final shape
As a polypeptide chain grows longer, it begins to fold into any of a variety of complex shapes.

Entire coil folds to form a globular structure.
Protein strands in muscle fibers are much longer than they are wide, allows muscle fibers to contract and relax. Actin and myosin.
Red blood cells being shaped like flattened discs with depressed centers (like a throat losenge). Allows shape to change so blood can flow.

Amino Acid Structure

  • Central carbon atom bonded to a hydrogen atom
  • Nitrogen-containing amino group
  • Carboxylic acid group
  • A side chain (R-group)
Most amino acids have three common parts:
• A central carbon atom bonded to a hydrogen atom
• A nitrogen-containing amino group (-NH2)
• A carboxylic acid group (-COOH)

Each amino acid also contains a side chain (R Group).
• The side chain or R-group: varies in size and structure; gives the amino acids their unique properties.
• The structure of the R-group can be as simple as a single H, or as complex as a ring structure
Photo by widdowquinn

The body needs 20 amino acids to make all the proteins it requires, and these amino acids can be categorized into: essential, non-essential and conditionally essential.

Essential Amino Acids

  • Amino acids that cannot be synthesized by the body in sufficient amounts to meet its needs.
  • Must be included in the diet
  • Also call indispensable amino acids
  • 9 amino acids are needed by the adult human body
The healthy adult body either cannot make these amino acids or can not make them in sufficient amounts.
Listed on page 193 of your text book.

Non-Essential Amino Acids

  • Can be made in the body
  • Also called dispensable amino acids
  • 11 amino acids are considered non-essential
To synthesize a non-essential amino acid, the body transfers an amino group from one amino acid to another compound (called an alpha-keto acid) which is basically an amino acid without its amino group. This process is called transanimation and results in the synthesis of a new amino acid

Transanimation. Our bodies can make nonessential amino acids by transferring the amine group from an essential amino acid to a different acid group and side chain.
The acid groups and side chains can be donated by amino acids, or they can be made from the breakdown products of carbohydrates and fats.
Photo by coofdy

Conditionally Essential

  • Under certain conditions, some of the nonessential amino acids cannot be synthesized in sufficient amounts to meet needs.
A baby born with PKU cannot metabolize phenylalanine (essential amino acid) and the body uses phenylalanine to synthesize tyrosine so without phenylalanine tyrosine becomes essential. Can lead to irreversible brain damage if not found early. Lacking phenylalanine hydroxylase.
Glutamine -
Photo by anieto2k

Protein Sources

Animal Sources and Plant Sources
Photo by Nanagyei

Animal Sources

  • Contain the most concentrated sources of proteins in our diet - greater amounts of essential amino acids
  • Provide B vitamins and readily absorbable minerals such as iron, zinc and calcium
  • Low in fiber
  • High in Saturated fat and cholesterol
Photo by tarale

Plant Sources

  • Provide most, but not all B vitamins.
  • Also supply iron, zinc and calcium in less absorbable forms
  • Sources of fiber, phytochemicals and unsaturated fats
Vegetarian diets can be healthy, but vegetarians, and vegans need to make sure they are getting enough B12, calcium, iron and zinc. B12 is found naturally only in animal products
Photo by Dey

Are all Food Proteins Created Equal?

  • Complete protein sources: Those containing adequate amounts of all essential amino acids
  • Incomplete protein sources: Those containing low amounts of one or more essential amino acids.

Protein Complementation

  • Combining a variety of foods with incomplete proteins can provide adequate amounts of all essential amino acids
  • Customary around the world, particularly in regions that rely heavily on plant sources for proteins
  • Examples: Rice and beans, rice and corn

Denaturation

  • Alteration of a protein’s three-dimensional structure - altered shape = altered function
  • Caused by: Heat, acids, bases, salts, mechanical agitation
  • Examples: Cooking, digestion
Denaturation: think of a paper fan, being unfolded.... can't work as a fan anymore

When an egg is cooked, the heat denatures the protein, causing the polypeptide chain to unfold. The protein in a raw egg white forms a clear viscous liquid, but when the heat denatures it, the cooked egg white becomes firm, and cannot be restored to its original form.

The denaturation of proteins in our food also create other characteristics we desire. For example whipped cream is made when mechanical agitation denatures the protein in the cream

During digestion, the salivary amylase, ,which is a protein, enters the stomach, the acid causes the structure of the protein to change, and it no longer functions in the digestion of starch.
Photo by RLHyde

Protein Digestion and Absorption

How are dietary proteins digested, absorbed and circulated?
The process of digestion disassembles food proteins into amino acids that are then absorbed and circulated into cells where the amino acids are reassembled into the proteins that the body needs. Think about dissembling a house, then using the materials to rebuild another house that perfectly fits your own exact needs. In addition to using dietary proteins, the body efficiently breaks down and recycles its own proteins then they become old or non-functional

Protein Digestion Begins in the Stomach

  • Chemical digestion begins in the acid environment of the stomach.
  • HCl denature proteins, opening up their folded structure making polypeptide chains more accessible to breakdown by enzymes
  • HCl converts pepsinogen to the active enzyme pepsin, break down the peptide bonds between amino acids
The presence of food in your stomach, causes some gastric cells to release the hormone gastrin, which is released from endocrine cells found deep in gastric pits

Gastrin triggers the release of HCl, pepsiongen, mucus, and substances from other stomach cells. These are collectively called "gastric juices"

HCl denature proteins, opening up their folded structure making polypeptide chains more accessible to breakdown by enzymes

HCl converts pepsinogen to the active enzyme pepsin, break down the peptide bonds between amino acids

As a result of the actions of the gastric juices, proteins you eat are partially digested to shorter peptides, and some free amino acids. The partially broken down proteins are then ready to leave the stomach and enter the small intestine to be digested further
Photo by camerakarrie

Protein Digestion Continues in Small Inestine

  • Most protein digestion occurs in the small intestine
  • Polypeptides are broken into even smaller peptides and amino acids by protein-digesting enzymes in the pancreas and small intestine
  • Single amino acids, dipeptides and tripeptides are absorbed into the mucosal cells of the small intestine

Absorption and Circulation

  • Amino acids from protein digestion enter your body by crossing the lumen of the small intestine into the mucosal cells and then into the blood
  • Most amino acids are abosrbed in the duodnenum, where they enter your blood and circulate to your liver via the hepatic portal system
When protein digestion is complete, some amino acids are already in the enterocytes (cells that line the intestine). However, those remaining in the intestinal lumen must be transported into the brush border cells. This process one of several energy-requiring amino acid transport system (passive and active transport mechnaisms). Because amino acids with chemicalyl similar R-groups are often transported by the same carrier molecules, such amino acids compete with each other for transport into the blood. If there is an excess of any one of the amino acids sharing transport systems, more of it will be absorbed, slowing transport of another. This competition of amino acids is not usually a problem because foods contain a variety of amino acids, none of which are present in excessive amounts. However, when people consume amino acids supplements, the supplemented amino acid may overwhelm the transport system, reducing the absorption of other amino acids that share the same transport system.
Photo by euthman

Protein Functions in the Body

  • Structure
  • Catalysis
  • Movement
  • Transport
  • Communication
  • Protection
  • Regulation of fluid balance and pH
Structure: Proteins provide most of the structural materials in the body, being constituents of the muscles, skin, bones, hair and fingernails. Example: collagen is a structural protein that forms a supporting matrix in bones, teeth, ligaments and tendons. Proteins are also important structural components of cell membranes and organelles

Catalysis: Enzymes (most of which are protein) function as biological catalysts, and speed up chemical reactions that occur in our body. Example: Pepsin digests proteins in the small intestine. Analogy: Consider everything it takes to prepare a meal. Chemical reactions (like meals) will not occur readily without enzymes (chefs) to arrange the molecules in the correct positions

Movement: Some proteins have contractile properties muscles and ligaments to move various parts of the body. Example: Actin and myosin in muscle, make up much of the machinery needed to contract muscles, this is why protein deficiency may cause muscle wasting and weakness

Transport: transport proteins involved in the movement of substances across cell membranes and within the circulatory system. Example: glucose transporters which move glucose from blood to tissues.

Communication: Protein hormones, and cell-signaling proteins regulate biological processes. Example: Insulin and glucagon regulate blood glucose

Protection: Skin proteins and immune proteins. Skin is the first barrier against infection or injury. Foreign particles on the skin such as dirt and bacteria can not penetrate. If skin is broken, and blood vessels are injured, blood clotting proteins help prevent too much blood from being lost. If foreign material does get in, antibodies, which are immune system proteins help destroy it.

Regulation of fluid balance: Proteins, via the process of osmosis, regulate the distribution of fluid in the body's various compartments. Example: Albumin is a major regulator of fluid balance inthe circulatory system

Regulation of pH: The chemical reactions of metabolism require a certain pH (acidity) to function properly. Proteins that readily take up and release Hydrogen ions (H+) mainatin normal (relatively neutral) pH of the body. Example: Hemoglobin is an important regulator of blood pH
Photo by profzucker

Structure

  • Proteins provide most of the structural materials in the body, being constituents of the muscles, skin, bones, hair and fingernails.
  • Proteins are also important structural components of cell membranes and organelles
Structure: Proteins provide most of the structural materials in the body, being constituents of the muscles, skin, bones, hair and fingernails. Example: collagen is a structural protein that forms a supporting matrix in bones, teeth, ligaments and tendons. Proteins are also important structural components of cell membranes and organelles
Photo by El Bingle

Catalysis

  • Enzymes (most of which are protein) function as biological catalysts, and speed up chemical reactions that occur in our body.
Catalysis: Enzymes (most of which are protein) function as biological catalysts, and speed up chemical reactions that occur in our body. Example: Pepsin digests proteins in the small intestine. Analogy: Consider everything it takes to prepare a meal. Chemical reactions (like meals) will not occur readily without enzymes (chefs) to arrange the molecules in the correct positions
Photo by Enzymlogic

Movement

  • Some proteins have contractile properties, such (muscles and ligaments) to move various parts of the body
Movement: Some proteins have contractile properties muscles and ligaments to move various parts of the body. Example: Actin and myosin in muscle, make up much of the machinery needed to contract muscles, this is why protein deficiency may cause muscle wasting and weakness

Transport

  • Transport proteins are involved in the movement of substances across cell membranes and within the circulatory system.
Transport: transport proteins involved in the movement of substances across cell membranes and within the circulatory system. Example: glucose transporters which move glucose from blood to tissues.
Photo by stimpsonjake

Communication

  • Protein hormones, and cell-signaling proteins regulate biological processes.

Communication: Protein hormones, and cell-signaling proteins regulate biological processes. Example: Insulin and glucagon regulate blood glucose
Photo by Stéfan

Protection

  • Skin is the first barrier against infection or injury
  • If skin is broken, and blood vessels are injured, blood clotting proteins help prevent too much blood from being lost
  • If foreign material does get in, antibodies, which are immune system proteins help destroy it.
Protection: Skin proteins and immune proteins. Skin is the first barrier against infection or injury. Foreign particles on the skin such as dirt and bacteria can not penetrate. If skin is broken, and blood vessels are injured, blood clotting proteins help prevent too much blood from being lost. If foreign material does get in, antibodies, which are immune system proteins help destroy it.
Photo by chexee

Regulation of Fluid Balance and pH

  • Proteins regulate the distribution of fluid in the body's various compartments.
  • Proteins that readily take up and release Hydrogen ions (H+) maintain normal (relatively neutral) pH of the body.
Regulation of fluid balance: Proteins, via the process of osmosis, regulate the distribution of fluid in the body's various compartments. Example: Albumin is a major regulator of fluid balance inthe circulatory system

Regulation of pH: The chemical reactions of metabolism require a certain pH (acidity) to function properly. Proteins that readily take up and release Hydrogen ions (H+) mainatin normal (relatively neutral) pH of the body. Example: Hemoglobin is an important regulator of blood pH

If protein levels in the blood fall too low, water leaks out of the blood vessels and accumulates in the tissues, causing swelling known as edema
Photo by mr.beaver

Protein as a Source of Energy

  • The body can use some amino acids for glucose synthesis and energy (ATP) production
  • Amino acids can be converted to fatty acids, which are stored as triglycerides, and can contribute to weight gain
In addition to all of the essential functions mentioned, under some circumstances, proteins can be broken down and their amino acids used to provide energy or synthesize glucose or fatty acids.

Because extra amino acids can't be stored, they are metabolized to provide energy. When your diet provides more protein energy then it needs, amino acids are converted to fatty acids and stored as triglycerides
Photo by Caucas'

Synthesizing Proteins

  • The instructions for making proteins are contained in the nucleus of the cell in stretches of DNA called genes
  • When protein is needed the process of protein synthesis begins, and the information in the gene is used to make the protein
Figure 6.6, Pg 165
Photo by M Pinarci

Recommended Protein Intake

  • The RDA for protein for most healthy adults is 0.8g/kg of body weight (to convert lbs. to kg, divide your weight in pounds by 2.2)
  • Minimum of 10% of total calories
RDAs are based on body weight, so it varies significantly from person to person

During certain life stages (infancy, pregnancy, lactation) protein needs are increased to support growth and milk production

For a variety of reasons, people recovering from trauma, such as burn victims, or illness may require more protein

Athletes may require more protein, but this is a topic of active debate.
Photo by bark