Protein: Amino Acids Copyright 2005 Wadsworth Group, a division of Thomson Learning

Amino Acids Copyright 2005 Wadsworth Group, a division of Thomson Learning

Amino Acids Nonessential amino acids –a.k.a dispensable amino acids Essential amino acids –a.k.a indispensable amino acids Conditionally essential amino acids Copyright 2005 Wadsworth Group, a division of Thomson Learning

An Essential Amino Acid

Nonessential Amino Acids

P roteins Peptide bond Dipeptide – 2 amino acids Copyright 2005 Wadsworth Group, a division of Thomson Learning

Proteins Tripeptide amino acidDipeptide+ Tripeptide 3 amino acids Oligo peptide (oligo = few) 4 to 9 amino acids

Proteins Polypeptide Copyright 2005 Wadsworth Group, a division of Thomson Learning

Proteins Amino acid sequences –In starches and fatty acids lengthening the chain just meant adding more units of the same (glucose in starch or 2 carbon compounds in fatty acids) E.g. The sequence of a starch molecule would read glucose-glucose-glucose Where as a the sequence of a protein molecule could read –Methionine-Valine-Glycine….. OR –Histidine-Aspartic acid-Isoleucine-Valine….. –Since there are 20 different amino acids what determines which amino acid is added next to the chain? Copyright 2005 Wadsworth Group, a division of Thomson Learning

Animal Cell Features Nucleus (DNA) –Has the chromosome which is made up of DNA –DNA carries the instructions for making every protein in your body –The proteins (as enzymes) in turn are involved in synthesizing everything else in your body RNA Ribosomes Figure 4.10b Page 61

Protein Synthesis Delivering the instructions –DNA is the repository of all the information needed to form a cell or an individual mRNA is the instructions for each protein It is like copying out a single chapter or part of a chapter from a book Each chapter is roughly equivalent to a gene Ribosomes, tRNAs etc are like the tools that would use to make the item This process is called gene expression Every cell in your body has all of your genes, the fact that your skin cell looks different from your nerve cell is because one set of genes are expressed in your skin cells and a different set of genes are expressed in your nerve cells. For e.g. Copyright 2005 Wadsworth Group, a division of Thomson Learning

DNA RNA Knitting Instructions Sizes: Child’s sizes 2 (4, 6, 8, 10) Yarn: 4-medium worsted-weight wool or acrylic Amount: 9 (10, 12, 14, 16) ounces Total Yardage: 525 (580, 700, 715, 935) yards Gauge: 5 stitches = 1 inch; 20 stitches = 4 inches Needle Size: US Size 7 (4.5 mm) for body & US Size 5 (3.75 mm) for bottom border. Back and Front (make 2): With #5 needles, cast on 66 (70, 74, 78, 82) stitches. Knit rows 1-10 (garter stitch) for bottom border. Switch to #7 needles and work in stockinette stitch (knit one row, purl 1 row) until piece measures 81/2" (91/2", 101/2", 111/2", 121/2") from cast-on edge. End by working a purl row. Sleeves: This pattern requires on edge stitch for the sleeves—this means you must always knit the first and last stitch of every row. Row 1: Add on 28 (30, 32, 34, 36) stitches loosely for the first sleeve and knit across 94 (100, 106, 112, 118). Row 2: Add on 28 (30, 32, 34, 36) stitches loosely for the second sleeve and purl across (remember to knit first and last stitches of every row). You should now have a total of 122 (130, 138, 146, 154) stitches. Continue in stockinette stitch until sleeve measures 51/2" (6", 61/2", 7", 71/2"). End by working a purl row. Bind off loosely Protein

Protein Synthesis Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Synthesis Copyright 2005 Wadsworth Group, a division of Thomson Learning Peptide bond Dipeptide Tripeptide

Protein Synthesis Copyright 2005 Wadsworth Group, a division of Thomson Learning Polypeptide OR Protein strand

Protein Synthesis Why is the order so important? –The sequence of amino acids in the protein decides how the protein folds up. –How the protein folds up determines whether or not or how well it will function. Sequencing errors Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein shape and function

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Proteins Protein denaturation –Proteins that have folded into their proper structure can perform their function –If a protein is exposed to heat, acid or other conditions it will denature i.e. it will uncoil and lose its shape and no longer be able to function –Beyond a certain point denaturation is irreversible –This happens when we cook an egg, or curdle milk or beat egg whites into stiff peaks –The acid in your stomach also denatures proteins –When we cook we don’t care that these proteins cannot perform their natural function because we are more interested in altering its texture and inside our bodies in getting the amino acids broken apart to make our proteins Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Synthesis Nutrients and gene expression –Cells can regulate gene expression to make the types of proteins that they need –For e.g. cells of the pancreas make insulin but not the cells of your intestine –Nutrients can play a key role in deciding whether or how much a gene is expressed i.e. how many copies of a particular protein is made. Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Digestion Stomach –HCl Denatures proteins so they can be broken down by enzymes –Pepsinogen  pepsin Proenzyme – inactive enzyme so it doesn’t digest the cells that produce it Notice that pepsin is also a protein but because of the sequence of its amino acids it does not get denatured by the acid in the stomach but cuts up other proteins When it moves into the small intestine along with the food, it too will be digested as protein Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Digestion Small intestine –Proteases Digest complete proteins or large peptides Intestinal and pancreatic –Peptidases Tripeptidases Dipeptidases Break tri and dipeptides down into amino acids Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Digestion in the GI Tract

Protein Absorption Carriers –Transport amino acids, dipeptides and tripeptides into the intestinal wall cells –Some can be used directly by these cells for energy or making proteins Capillaries –The remaining are transported to the rest of the body (first to the liver) through the circulatory system Absorption misconceptions –Enzyme Almost all the enzymes in your food get digested as proteins they cannot continue to function in your body –amino acid supplements Your body does not need any help in digesting proteins so predigested supplements are unnecessary Copyright 2005 Wadsworth Group, a division of Thomson Learning