Proteins– Monomer: Amino acids– Polymer: Polypeptide (aka protein)– Key Elements: C, H, N, “R” (R varies)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Proteins are:a) Hydrophobicb) Hydrophilicc) Could be eitherd) Not sure

Protein Functions

• Proteins are >50% of the dry mass of most cells– Structural support– Storage– Transport– Cellular communications– Movement– Defense against foreign substances– ALL enzymes are proteins – chemical reactions wouldn’t

occur in our cells without proteins!

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Proteins have many diverse functions; they are the most functionally diverse type of macromolecules

1. Structural support (e.g. silk of spider webs)

2. Storage of energy & nitrogen (e.g. egg albumin)

3. Transport of substances within organisms(e.g. hemoglobin) or across membranes (e.g. aquaporins)

4. Signaling: long-distance (e.g. insulin) or short-distance; gene-regulatory proteins; receptor proteins

Functions of Proteins: Examples

Functions of Proteins: Examples

Proteins have many diverse functions; they are the most functionally diverse type of macromolecules

5. Defense against invading pathogens (e.g. antibodies in immune system)

Antibody protein Protein from flu virus

6. Movement (e.g. muscle proteins) ATP Actin and Myosin

Fig. 8.16

Enzymes speed up chemical reactions

7. Metabolic catalysts (enzymes)

Beans and otherlegumes

Corn (maize)and other grains

Lysine

Essential amino acids

Tryptophan

Isoleucine

Leucine

Phenylalanine

Threonine

Valine

MethionineFig. 41.2

So, a diet of only wheat bread and corn would not be sufficient.

Peptide bond is C-N bond between neighboring amino acids formed by removal of H2O (dehydration synthesis).

Since amino acids in proteins are bonded together by peptide bonds, proteins are also called polypeptides.

Peptidebond

Peptidebond

Side chains

Backbone

Fig. 5.18

Levels of protein structure

Fig. 5.21

PrimaryStructure

SecondaryStructure

TertiaryStructure

pleated sheet

Examples ofamino acidsubunits

helix

QuaternaryStructure

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Exact sequence of amino acids is called the primary structure of a protein.

Fig. 5.21

Amino acidsubunits

25

20

15

10

5

1

Primary Structure

Levels of protein structure

Fig. 5.21

PrimaryStructure

SecondaryStructure

TertiaryStructure

pleated sheet

Examples ofamino acidsubunits

helix

QuaternaryStructure

Fig. 5.21

Secondary Structure

pleated sheet

helix

Secondary structure:Helix or pleated sheet.

Pleated sheet protein often used for structural purposes

Spider’s abdominal glandssecrete silk fibers made

of structural proteinwith pleated sheets.

Fig. 5.21

Levels of protein structure

Fig. 5.21

PrimaryStructure

SecondaryStructure

TertiaryStructure

pleated sheet

Examples ofamino acidsubunits

helix

QuaternaryStructure

Polypeptidebackbone

Tertiary structure results from various kinds of interactions between atoms of the side chains (R groups).

Fig. 5.21

Levels of protein structure

Fig. 5.21

PrimaryStructure

SecondaryStructure

TertiaryStructure

pleated sheet

Examples ofamino acidsubunits

helix

QuaternaryStructure

Polypeptidechain

Chains

HemeIron

Chains

CollagenHemoglobin Fig. 5.21

Quarternary structure is

the interaction of different subunits.

Changes in primary structure can have a profound effect on protein function.

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules donot associatewith oneanother; eachcarries oxygen.

Normalhemoglobin(top view)

subunit

Normal hemoglobin

7654321

GluVal His Leu Thr Pro Glu

Fig. 5.22

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules doNot stickto eachother; eachcarries oxygen

Normalhemoglobin

subunit

Normal hemoglobin

7654321

GluVal His Leu Thr Pro Glu

Molecules crystallize into fiber; capacity to carry oxygengreatly reduced

Sickle-cellhemoglobin

Sickle-cell hemoglobin

7654321

ValVal His Leu Thr Pro Glu

Fig. 5.22

Exposedhydrophobicregion

Nonpolar R groups: hydrophobic

Glycine Alanine Valine Leucine Isoleucine

Fig. 5.17Amino acid R (rest) groups

Arginine HistidineAspartic acid Glutamic acid Lysine

ElectricallyCharged

R groups:hydrophilic

Primarystructure

Secondaryand tertiarystructures

Function

Quaternarystructure

Molecules doNot stickto eachother; eachcarries oxygen

Normalhemoglobin

subunit

Normal hemoglobin

7654321

GluVal His Leu Thr Pro Glu

Molecules crystallize into fiber; capacity to carry oxygengreatly reduced

Sickle-cellhemoglobin

Sickle-cell hemoglobin

7654321

ValVal His Leu Thr Pro Glu

Fig. 5.22

Exposedhydrophobicregion

Normal red bloodcells are full ofindividualhemoglobinmolecules, each carrying oxygen.

Fibers of abnormalhemoglobin deformred blood cells intosickle shape.

10 µm 10 µm

Fig. 5.22

The Genetics of Sickle Cell Anemia

• Sickle cell anemia is a recessive disorder.

• AA (homozygous dominant) don’t have symptoms.

• aa (homozygous recessive) have severe symptoms, including:

• Low body oxygen levels• Severe pain• Swelling of hands and feet• Frequent infections (spleen)• Delayed growth/development• Vision problems

• What about heterozygotes (Aa)?• Usually lack negative effects, but high stress situations can trigger symptoms

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Why hasn’t natural selection eliminated sickle cell anemia?

Some clues:• 1 in 10 African Americans is a carrier for sickle cell anemia• Rates of sickle cell anemia are also higher in people with Mediterranean, Middle Eastern, and Indian ancestry

• Individuals with two copies of the altered gene suffer many complications (pain, infections, stroke, etc.), but are

resistant to malaria. •Individuals with one copy suffer few complications and

are also resistant.

Sickle-cell disease inheritance.http://en.wikipedia.org/wiki/Sickle-cell_disease

0–2.5%

Distribution ofmalaria caused byPlasmodium falciparum(a parasitic unicellular eukaryote)

Frequencies of thesickle-cell allele

2.5–5.0%

7.5–10.0%

5.0–7.5%

>12.5%

10.0–12.5%

Fig. 23.17

“Heterozygote Advantage”

Nonpolar R groups: hydrophobic

Glycine Alanine Valine Leucine Isoleucine

Fig. 5.17Amino acid R (rest) groups

Arginine HistidineAspartic acid Glutamic acid Lysine

ElectricallyCharged

R groups:hydrophilic

Today’s Exit Ticket

The bonds creating the primary structure of a protein are called 1)___________ and form between a 2)___ atom in one amino acid and a 3)____ atom in another amino acid.

The bonds creating the secondary structure of a protein are called 4)__________ and form between 5)___________.

The bonds creating the tertiary structure of a protein can be covalent, ionic, or hydrogen bonds, and form between 6)_______________.

7) Describe the quaternary structure of a protein.