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

Protein: Amino Acids

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

Amino Acids


Amino Acids• Nonessential amino acids

– a.k.a dispensable amino acids

• Essential amino acids– a.k.a indispensable amino acids

• Conditionally essential amino acids


An Essential Amino Acid

Nonessential Amino Acids

Proteins• Peptide bond

• Dipeptide – 2 amino acids


Proteins

• Tripeptide

amino acidDipeptide +

Tripeptide3 amino acids

Oligo peptide (oligo = few)4 to 9 amino acids

Proteins• Polypeptide


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?


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 4.10bPage 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.


DNARNA

Knitting InstructionsSizes: Child’s sizes 2 (4, 6, 8, 10)Yarn: 4-medium worsted-weight wool or acrylicAmount: 9 (10, 12, 14, 16) ouncesTotal Yardage: 525 (580, 700, 715, 935) yardsGauge: 5 stitches = 1 inch; 20 stitches = 4 inchesNeedle 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 bottomborder. Switch to #7 needles and work in stockinette stitch (knit one row, purl 1 row) until piecemeasures 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 laststitch of every row. Row 1: Add on 28 (30, 32, 34, 36) stitches loosely for the first sleeve and knitacross 94 (100, 106, 112, 118). Row 2: Add on 28 (30, 32, 34, 36) stitches loosely for the secondsleeve and purl across (remember to knit first and last stitches of every row). You should now have atotal 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

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Protein Synthesis


Protein Synthesis


Peptide bond

Dipeptide Tripeptide

Protein Synthesis


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

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein shape and

function

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


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.


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


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


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


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

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