Regents Biology

Proteins

Regents Biology 2006-2007

Proteins:

Multipurpose molecules

Regents Biology

Functions of proteins/amino acids:

collagen (skin)

hemoglobin

 structural– claws, nails, hair, hooves (keratin), outer layer of skin (collagen)

transport - hemoglobin, cell membrane transport proteins

movement contractile proteins actin & myosin regulatory - hormones catalytic – enzymes that speed up reactions

allowing them to occur immunological – antibodies, antigens on the

exterior of a cell storage of amino acids

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Proteins

Building block =

aminoacid

aminoacid–

aminoacid–

aminoacid–

aminoacid–

—N—H

H

H|

—C—|

C—OH

||O

variable group

amino acids

20 different amino acids

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H

H

N C C

OH

O

H

R

amino group carboxyl group

R group

General structure of an amino acid

(basic) (acidic)

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You do NOT need to know their names!

There are 20 amino acids naturally incorporated into proteins

AlanineArginine

AsparagineAspartic acid

CysteineGlutamic acid

Glutamine

Glycine HistidineIsoleucineLeucineLysine

MethioninePhenylalanine

ProlineSerine

ThreonineTryptophan

TyrosineValine

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Other amino acids do exist…

CH2H

H

N C C

OH

O

H

O

II

II

Thyroxine:used in the human body as a hormone

to regulate metabolic rate

…but are not normally found in proteins

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Humans can synthesis some amino acids by altering other amino acids, however…

…some amino acids cannot be synthesised and are therefore needed in the diet.

These are the essential amino acids

ArginineHistidine

IsoleucineLeucine

LysineMethionine

Phenylalanine

ThreonineTryptophan

Valine

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Phenylketonuria or Maple Syrup Urine Disease

Patients lack the enzyme phenylalanine hydroxylase – needed to dispose of the amino acid phenylalanine properly

Penylalanine rapidly builds up in the blood stream

- it converted to unusual metabolites which give the patient’s urine a characteristic smell

- it also rapidly causes brain damage!

Treatment: A diet low in phelylalanine

No meat, fish, poultry, eggs, cheese, milk, beans, or peas

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Water-fearing amino acids Hydrophobic

“water fearing” amino acids try to get away from water in cell

the protein folds

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Different amino acids have different R groups

Their different properties depend on their R groups

Hydrophobic (‘Water-hating’) R groups

CH3H

H

N C C

OH

O

H

alanine

CH2H

H

N C C

OH

O

Hphenylalanine (aromatic)

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Water-loving amino acids Hydrophillic

“water loving” amino acids try to stay in water in cell

the protein folds

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Hydrophillic (‘Water-loving’) R groups

CH2H

H

N C C

OH

O

H

SH

cysteine

CH2H

H

N C C

OH

O

H

OH

serine

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Amino acid chains Proteins

amino acids chained into a polymer

Each amino acid is different some “like” water & dissolve in it

some “fear” water & separate from it

amino acid amino acid amino acid amino acid amino acid

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Formation of a dipeptide: carboxyl group of one amino acid reacts with amino group of second amino acid

H2Owater

molecule formed

H

H

N C C

OH

O

H

R2H

H

N C C

OH

O

H

R1

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

peptide linkage

a dipeptide

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H

H

N C C

OH

O

H

R1 H

H

N C C

OH

O

H

R2

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

H2O

Formation of a dipeptide produces

a molecule of water, therefore…

…this is a condensation

reaction

2 amino acids dipeptide + water

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H

H

N C C

OH

O

H

R1 H

H

N C C

OH

O

H

R2

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

H2O

Splitting a dipeptide to form two amino acids consumes one molecule of

water, therefore…

…this is a hydrolysis reaction

dipeptide + water 2 amino acids

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3-D protein structure

collagen

Proteins fold & twist into 3-D shape that’s what happens in the cell!

hemoglobingrowthhormone

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Its shape that matters! Proteins do their jobs, because

of their shape Unfolding a protein destroys its shape

wrong shape = can’t do its job unfolding proteins = “denature”

temperature pH (acidity) folded

unfolded“denatured”

Regents Biology 2006-2007

Let’s eat some

Proteins!