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Proteins Proteins (Polypeptides)(Polypeptides)

• Contain carbon, hydrogen, oxygen, nitrogen, and sulfur

• Basic building block is the amino acid• There are 20 different kinds of amino

acids• Amino acids are bonded together by

peptide bondspeptide bonds (polypeptidespolypeptides).

aa1 aa2 aa3 aa4 aa5 aa6

Peptide Bonds

Amino Acids (aa)

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Proteins Proteins (Polypeptides)(Polypeptides)

Six functions of proteins:Six functions of proteins:

1.1. StorageStorage :: albumin (egg white)albumin (egg white)

2.2. TransportTransport : : hemoglobinhemoglobin

3.3. RegulatoryRegulatory :: hormoneshormones

4.4. MovementMovement:: musclesmuscles

5.5. StructuralStructural :: membranes, hair, nailsmembranes, hair, nails

6.6. EnzymesEnzymes :: cellular reactionscellular reactions

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Proteins Proteins (Polypeptides)(Polypeptides)

Amino Acid

• Amine group acts like a base, tends to be positive.• Carboxyl group acts like an acid, tends to be negative.• “R” group is variable, from 1 atom to 20.• Two amino acids join together to form a dipeptide. • Adjacent carboxyl and amino groups bond together.

Some Amino Acids

Some More Amino Acids

Still More Amino Acids

Formation of a Dipeptide

Dehydration synthesis

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Proteins Proteins (Polypeptides)(Polypeptides)

Amino Acid + Amino Acid --> Dipeptide

Amino Acid + Dipeptide --> Tripeptide

A.A. + A.A. + …..+ Tripeptide --> Polypeptide

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Proteins Proteins (Polypeptides)(Polypeptides)

A protein consists of one or more polypeptide chains.

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Nucleic acidsNucleic acids• The chemical link between generationsThe chemical link between generations• The source of The source of genetic information in genetic information in

chromosomeschromosomes• Dictate Dictate amino-acid sequence in proteinsamino-acid sequence in proteins• Simple units called Simple units called nucleotidesnucleotides, connected , connected

in long chainsin long chains

Nucleic acids Nucleic acids are composed of long chainsof nucleotidesnucleotides linked by dehydration dehydration

synthesissynthesis.

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Nucleic acidsNucleic acids

• Two types:Two types:

a. Deoxyribonucleic acid a. Deoxyribonucleic acid (DNA-(DNA- double helix) double helix)

b. Ribonucleic acid (RNA-single b. Ribonucleic acid (RNA-single strand) strand)

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Nucleic acidsNucleic acidsNucleotidesNucleotides have 3 parts:have 3 parts:

1- 1- phosphate group (P)phosphate group (P)2- 2- pentose sugar (5-carbon)pentose sugar (5-carbon)3- 3- nitrogenous bases:nitrogenous bases:

adenine (A)adenine (A)thymine (T) DNA onlythymine (T) DNA onlyuracil (U) RNA onlyuracil (U) RNA onlycytosine (C)cytosine (C)guanine (G)guanine (G)

The P groups make the links that unite the sugars (hence a The P groups make the links that unite the sugars (hence a ““sugar-phosphate backbone”sugar-phosphate backbone”

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NucleotideNucleotide

OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

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SugarSugar(deoxyribose)(deoxyribose)

DNADNA Nucleotides NucleotidesComposition (3 parts):Composition (3 parts):

1- 1- DDeoxyribose sugar (eoxyribose sugar (no Ono O in 3 in 3rdrd carbon) carbon)2- Phosphate group2- Phosphate group3- 3- One of 4 types of basesOne of 4 types of bases (all containing (all containing

nitrogen): nitrogen): - Adenine- Adenine- - Thymine (Only in DNA)Thymine (Only in DNA)- Cytosine- Cytosine- Guanine- Guanine

RNARNA Nucleotides NucleotidesComposition ( 3 parts):Composition ( 3 parts):

1- 1- RRibose sugar (ibose sugar (with Owith O in 3 in 3rdrd carbon) carbon)2- Phosphate group2- Phosphate group3- 3- One of 4 types of basesOne of 4 types of bases (all containing (all containing

nitrogen): nitrogen): - Adenine- Adenine- - Uracyl (only in RNA)Uracyl (only in RNA)- Cytosine- Cytosine- Guanine- Guanine

DNA DNA vs vs RNARNA

• DNADNA1- 1- DDeoxyribose sugareoxyribose sugar2- Bases: Adenine, 2- Bases: Adenine, ThymineThymine, Cytosine, , Cytosine, GuanineGuanine3- 3- DoubleDouble-stranded helix arrangement-stranded helix arrangement

• RNARNA1- 1- RRibose sugaribose sugar2- Bases: Adenine, 2- Bases: Adenine, UracylUracyl, Cytosine, Guanine, Cytosine, Guanine4- 4- SingleSingle stranded stranded

The Double Helix (DNA)The Double Helix (DNA)Structural model:Structural model:

• Model proposed by Watson & Crick, 1953Model proposed by Watson & Crick, 1953• Two sugar-phosphate strands, next to each other, Two sugar-phosphate strands, next to each other,

but running in opposite directions.but running in opposite directions.• Specific Hydrogen bondsSpecific Hydrogen bonds occur among bases from occur among bases from

one chain to the other:one chain to the other: A---TA---T , , C---GC---G

Due to this specificity, a certain base on one strand Due to this specificity, a certain base on one strand indicates a certain base in the otherindicates a certain base in the other. .

• The 2 strands intertwine, forming a double-helix The 2 strands intertwine, forming a double-helix that winds around a central axisthat winds around a central axis

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DNA - double helixDNA - double helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

How DNA WorksHow DNA Works1- 1- DNA stores genetic information in DNA stores genetic information in

segments called segments called genesgenes2- The DNA code is in 2- The DNA code is in TriTriplet Codonsplet Codons (short (short

sequences of sequences of 33 nucleotides each) nucleotides each)3- Certain 3- Certain codonscodons are translated by the cell are translated by the cell

into into certain Aminocertain Aminoacids.acids.4. Thus, the 4. Thus, the sequence of nucleotidessequence of nucleotides in DNA in DNA

indicate a indicate a sequence of Amino acidssequence of Amino acids in a in a proteinprotein..