Proteins Ppt. (by Cdm)

8/11/2019 Proteins Ppt. (by Cdm)

1/31

By

Christian D. Magdale

1


2/31

I. INTRODUCTION

Proteins

* From Greek word ---> of first importance

* Composed of: C, H, O, N, S*The most abundant & versatile molecule within

the cell

2


3/31

II. CELLULAR FUNCTIONS OF PROTEINS1. Enzymes

2. Antibodies* Help fight infection

3. Transport Proteins

* Ex.: Transferrin ---> Iron--> bone marrow --> heme

Hemoglobin & myoglobin4. Regulatory proteins (hormones)

5. Structural proteins

* Ex.: keratin, tendon, & cartilage

6. Movement proteins* Ex.: actin, myosin , flagellum

7. Nutrient proteins

* egg albumin (for embryos), milk casein ( for infants)3


4/31

III. AMINO ACIDS: THE MONOMERS OF

PROTEINSGeneral Structures of

Amino acids

1. -Carbon (centralcarbon)

2. -Carboxylate group

* a carboxyl group thathas lost a proton (-C00-)

3. -Amino group* an amino group that has

gained a proton (-NH3+)

4. Hydrogen atom

5. R group (side chain) 4


5/31

In a protein the R groups interact with one

another thru a variety of weak forces. These

interactions participate in folding the proteinchain into a precise 3-D shape that determines

its ultimate functions. They also serve to

maintain the 3-D conformation.

5


6/31

Enantiomers of Amino

Acids

1. L- amino acids

* -amino group on the

left side.

2. D- amino acids

* -amino group on the

right side.

6


7/31

Types of Amino Acids Based on the Polarity of the

Side chain Amino acids

Hydrophobic (Non-polar) AminoAcids

* Prefer contact w/ one another

over water

* Generally found in the interior of

proteins to remain isolated w/

water

Hydrophilic (Polar)Amino Acids

* Prefer contact w/ water

Their hydrophilic R groups are

found on the surfaces of proteins

Neutral Amino Acids

* Their R groups havehigh affinity for

water, but not

ionic at pH 7

Positively - Charged Amino

Acids

* At pH 7, they have a net +charge because their R

groups have + groups

* Basic because their R

groups react w/ water to

pick up a proton &

release a hydroxide ion

Negatively - Charged

Amino Acids

* At pH 7, they have a net

charge of -1.

* Have ionized carboxyl

groups (Carboxylate) in

their side chains.

* Acidic because ionization

of the carboxylic acidreleases a proton (H+)

7


8/31

8


9/31

IV. THE PEPTIDE (POLYMER)

1. A peptide is a chain of two or more amino acidsconnected together by peptide bonds.

* The number of amino acids is indicated by prefixes

di-(2), tri-(3), tetra-(4), and so forth.* Long peptides are usually called polypeptides.

* A protein may be composed of one or more

peptides.

9


10/31

2. A peptide bond (amide bond) is formed when

the carboxyl group (Carboxylate group) of one

amino acid is linked to the amino group ofanother amino acid.

Illustration:

10
http://www.molecularstation.com/molecular-biology-images/data/510/PeptideBond-.jpg


11/31

3. A peptide has two ends:

a. Amino(N)terminal amino acid

* This is the end w/ a free -NH3+

b. Carboxy (C)terminal amino acid

* This is the end w/ freeCOO-

Illustration:

11
http://www.molecularstation.com/molecular-biology-images/data/510/PeptideBond-.jpg


12/31

4. Peptides are named as derivatives of the C-terminal

amino acids, which receives its entire name. For all

other amino acids in a peptide, the ending

ine ischanged toyl.

Example:

12

Glycine Alanine Glycyl-alanine (gly-ala)


13/31

V. WRITING THE STRUCTURES OF

SMALL PEPTIDES

Steps:

1. Note that the backbone of any peptide has the followingrepeating sequence from left to right:

N--C--C--N--C--C--N--C--C

1 2 1 2 1 2

2. In the sequence above, consider the followingdesignations:

N = the amino group

C-1 = the -carbon, which is always bonded to the hydrogenatom & the R group.

C-2 = the carbon of the carboxyl group, which is alwaysbonded to the oxygen atom

13


14/31

Example: Draw the structure of the tripeptide

alanyl-glycyl-valine.

Solution:

1. Write the backbone of the said tripeptide.

There are three sets. Remember that the N-

terminal amino acids is written to the left.

14

N--C--C N--C--CN--C--C

Set 1 Set 3Set 2


15/31



Solution:

2. Add oxygen to the carboxyl carbon & hydrogens

to the amino nitrogen

N--C--C--N--C--C--N--C--C

15


16/31



Solution:

3. Add the hydrogens to the -carbon.

N+--C--C--N--C--C--N--C--C--

16

H

H

H Oll

H

llO

H

llO

O-l

lll--


17/31



Solution:

4. Add the side chains. In the given example, they are CH3, -H, and CH(CH3)2

[from left to right]

N+--C--C--N--C--C--N--C--C--

17

H

H

H Oll

H

llO

H

llO

O-l

lll--

H H Hl l l


18/31

VI. LEVELS OF PROTEIN STRUCTURES

1. Primary structure

* The specific sequence of amino

acids

*Each protein has a unique

sequence.

18


19/31

2. Secondary structure

* The precise coiling & folding of the

primary structure, resulting from

the hydrogen bonding between

amide hydrogen & carbonyl oxygen

2.1. -helix

* The coiling of the primary structure

* Ex.: keratin (fibrous) (in hair, fur,

wool, & hoof)Myosin (fibrous) (in muscles)

2.2. -pleated sheets

* The folding of the primary structure

* Ex.: silk fibroin (fibrous protein fromsilk worm)

NOTE: a protein may be a mixture of -

helix & -pleated sheets

19


20/31

3. Tertiary structure (3-D structure)

* The further coiling & folding of the

secondary structures, giving the protein itsdistinct shape.

* Determines the specific functions of a protein

20

Tertiary structure


21/31

4. Quarternary structure

* The association of several polypeptides since

many proteins are not only composed of asingle peptide/polypeptide

* Sometimes, the quarternary structure binds

w/ a non-protein group (prosthetic group)which can modify the function/s of a protein.

* Ex.: Glycoprotein, lipoprotein, & hemoglobin

21


22/31

VII. HEMOGLOBIN VS. MYOGLOBIN

22

Hemoglobin

(a protein w/

iron

Myoglobin

(a protein w/

iron)

RBC Muscle

To transportoxygen

To storeoxygen

Myoglobin has greater affinity for oxygen than

hemoglobin! What is the advantage?


23/31

VIII. FETAL HEMOGLOBIN VS. ADULT

HEMOGLOBIN

Fetal hemoglobin has greater affinity for O2than

adult hemoglobin!

What is the advantage?

23


24/31

IX. PROTEIN DENATURATION

What is denaturation?This is a process wherein the coiling & folding of

proteins become disorganized. Denatured

proteins lose their functions.Can denaturation alter the primary structure of a

protein?

No, it cant!

24


25/31

Wh t th f t ( t ) th t t ib t t


26/31

What are the factors (agents) that can contribute to

protein denaturation?

3. Rubbing alcohol (2-propanol)

* Denatures protein by disrupting the hydrogen

bonds w/n the protein

* Traditionally, a 70% solution of rubbing alcohol has

been used as a disinfectant or antiseptic. However,

recent evidences suggest that it is not an effective

agent in this capacity.

4. Detergents

* They can disrupt the hydrophobic interactions,

causing the proteins to unfold.26

Wh t th f t ( t ) th t t ib t t


27/31

What are the factors (agents) that can contribute to

protein denaturation?

5. Heavy metals (Hg+and Pb+)

* They interfere with the salt bridges formed between

amino acid R groups of the chain, resulting in the

loss of conformation.

6. Mechanical stresses (stirring, whipping, & shaking)

* They can disrupt the weak interactions that

maintain the protein conformation. This is the

reason that whipping egg white produces a stiff

meringue.

27

X NUTRITIONAL CLASSES OF AMINO


28/31

X. NUTRITIONAL CLASSES OF AMINO

ACIDS

28

Essential A.A.* Not

synthesized

by the body

& thus

required inthe diet

Non - essentialA.A.

* Synthesized bythe body &thus notrequired inthe diet

Semi - essentialA.A.

* Needed by

premature

infants & ill

adults

Isoleucine

Leucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan

Valine

Alanine

Arginine

Asparagine

Aspartate

CysteineGlutamate

Glycine

Histidine

Proline

Serine

Tyrosine

Cysteine

Tyrosine

NOTE: Histidine & arginine

are essential amino acids

for infants, but not for

healthy adults


29/31

X. NUTRITIONAL CLASSES OF PROTEINS

29

Therefore, What is

the good source of

protein, animal or

plant?


30/31

What is wrong with strict vegetarian diet?

It cant provide all the essential amino acids!

However, this ca be remedied by succotashdiet (staple diet of native Americans), which is

a mixture of corn (rich in methionine) and

bean (rich in lysine & tryptophan).

30


31/31

THANK YOU SO MUCH!

31

Proteins Ppt. (by Cdm)

Documents

Transcript of Proteins Ppt. (by Cdm)