Molecular Biology Lec.1 - PowerPoint Presentation

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Molecular Biology

Lec.1

Dr. Mohammed Hussein

M.B.Ch.B, MSC, DCH (UK), MRCPCH

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Molecular Biology

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Main Topics Nucleic acid structure and

organizationDNA replication and repairTranscription and RNA processingThe genetic code, mutation, and translation

Genetic strategies in therapeutics

Techniques

of genetic analysis

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Human Molecular Biology

Human Molecular Biology is an introduction to health and disease for the new generation of life scientists and medical students.Good health is a matter of having the right molecules in the right place at

the right

time.

This

may seem self-evident, but the idea that health is

determined mainly

by molecules has only gained acceptance in recent

years.

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Lecture 1

Nucleic acid structure and organization

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Objectives

By the end of this lecture, one should able to

Understand the concept of central dogma of molecular biology

Recognize the structure of the nucleic acids

Know the types of the nitrogenous bases present in the DNA and RNA

Understand the process of base pairing

Know how to use Chargaff's rule to calculate the amount of nitrogenous bases in DNA molecule

Understand the packaging of the DNA in the nucleus

Know the differences

between

heterochromatin and euchromatin

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Central Dogma of Molecular Biology

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An organism must be able to:Store

its genetic information.Preserve these information.Pass

that information along to future

generations

.

Express

that information as it carries out all the processes of life.

Central Dogma of Molecular Biology

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Central Dogma of Molecular

Biology

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DNA

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The Four Scientists who

discover the DNA

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Nucleic Acid Structure and

Organization

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Nucleic acids

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Nucleic Acids

RNA = Ribonucleic

A

cid

DNA

=

D

eoxyribo

n

ucleic

A

cid

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Nucleic Acid Structure

Nucleic acids are polymers of Nucleotides

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Nucleotide

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What is nucleotide?

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Nucleotide consist of three components:

Five-carbon sugar (pentose)

Nitrogenous base

Phosphate group

2

1

3

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Five-Carbon Sugars

(Pentose)

Nucleic acids are classified according to the pentose they contain. If the pentose is

:

Ribose

RNA

(

R

ibo

N

ucleic

A

cid

)

Deoxyribose

DNA

(

D

eoxyribo

N

ucleic

A

cid

)

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Numbers

The

numbers identifying the carbons of

the sugar

are labeled with “primes

”

Number 1 (1՜)

Number 2 (2՜)

Number 3 (3՜)

Number 4 (4՜)

Number 5 (5՜)

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Nitrogenous

Bases

Is an organic molecule

 

with

a

nitrogen

atom

 

that has

the chemical properties of a

base

Adenine

Guanine

Cytosine

Uracil

Thymine

Purines

Pyrimidines

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Nitrogenous

Bases

RNA

has A, G, C, U

DNA

has A, G, C, T

They are Pure As Gold

They are

CUTe

and thin

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Nitrogenous base is attached to the 1՜ carbon of the pentose sugar.

1

2

3

4

5

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Are polymers of nucleotides joined by: 3՜, 5՜-phosphodiester bonds; that is a phosphate group links

the 3՜ carbon of a sugar to the 5՜ carbon of the next sugar in the chain.

Nucleic Acids

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T

C

G

A

Base Sequence

The base sequence of a

nucleic acid strand is

written

in the:

5

՜→3՜ direction (left to right).

Example:

5

՜-

TCGA-3

՜ or

TCGA

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DNA is double-stranded (dsDNA) RNA is single-stranded

(ssRNA)

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The double-stranded DNA (dsDNA)

The two strands are

antiparallel

(opposite in direction)

The two strands are

complementary

A

always pairs with

T

G

always pairs with

C

Thus, the base sequence on one strand defines the base sequence on the other strand.

Purine with Pyrimidine

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A

=

T

G

=

C

Adenine

Guanine

Thymine

Cytosine

Purine

Pyrimidies

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MNEMONIC

A always pair with T (both letters are of straight lines)G always pair with

C

(both letters are of

curved

lines

)

A bind to T by 2 bonds ( A to T by 2)

G bind to C by 3 bonds ( G to C by 3)

C and T are single rings (cute are thin), while A and G are double rings

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Deoxyribose Sugar

Phosphate group

A T

A T

A T

A T

C

G

C

G

C

G

C

G

T

A

T

A

G

C

C

G

T

A

A

T

G

C

C

G

C

U

T

E are thin

A to T by 2

G to C by 3

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Erwin Chargaff

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Erwin ChargaffChargaff discovered two 

rules that helped lead to the discovery of the double helix structure of DNA.

The

first rule was that in DNA the number of guanine units is equal to the number of cytosine units, and the number of adenine units is equal to the number of thymine units. This hinted at the base pair makeup of DNA.

The

second rule was that the relative amounts of guanine, cytosine, adenine and thymine bases vary from one species to another. This hinted that DNA rather than protein could be the genetic material.

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Chargaff’s

Rule

% A = % T

and

% G = % C

Example

a

sample of DNA has 10% G; what is the % T

?

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% G = % C, as G= 10% so C= 10% %G + %C = 20% therefore, % A + % T must total 80%40% A and 40% TAnswer: 40% T

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DNA HelixMost DNA occurs in nature as a right-handed double-helical molecule known as Watson-Crick DNA or B-DNA. There are about

10 base pairs per complete turn of the helix.

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Organization of

DNA

Large DNA molecules (about 2 meters length) must be packaged in such a way that they can fit inside the nucleus (about 6 µm) and still be

functional

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1/3,000,000

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NucleosomeNuclear DNA associated with histones and nonhistone proteins

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Cells in interphase contain two types of chromatin: Euchromatin (more opened and available for gene expression)

Heterochromatin (much more highly condensed and associated with areas of the chromosomes that are not expressed.)

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