Nucleic acids

Nucleic AcidsNucleic AcidsDNA and RNADNA and RNA

Hundreds of thousands of proteins exist inside each one of us to help carry out our daily functions. These proteins are produced locally, assembled piece-by-piece to exact specifications

This information, detailing the specific structure of the proteins inside of our bodies, is stored in a set of

molecules called nucleic acids.

Nucleic Acids DNA and RNA

DNA - deoxyribonucleic acid

RNA - ribonucleic acid

DNA- stores genetic information

RNA - use in protein synthesis

for putting genetic information

COMPOSITION OF NUCLEIC ACIDS

Nucleic Acids are POLYMERS

Proteins are polypeptides,

Carbohydrates are polysaccharides

Nucleic acid is polynucleotide- made of

NUCLEOTIDES

Structure of NUCLEOTIDE

The deoxyribonucleic acid, DNA, is a long chain of nucleotides which consist of

– Deoxyribose (a pentose = sugar with 5 carbons)

– Phosphoric Acid

– Organic (nitrogenous) bases (Purines - Adenine and Guanine, or Pyrimidines -Cytosine and Thymine

7

The Structure of Nucleic Acid

Nucleic Acid is a polymer of nucleotides

It is a very large molecule that have two main parts. The backbone of a nucleic acid is made of alternating sugar and phosphate molecules bonded together in a long chain phosphodiester bonds.

Each of the sugar groups in the backbone is attached (via the bond shown in blue) to a third type of molecule called a nucleotide base.

The Structure of Nucleic Acids

The phosphodiester bonds link the 3' carbon in the sugar ring of one nucleotide to the 5' carbon on the next nucleotide

sequence of bases constitutes the genetic information

Different pentose sugars in RNA & DNA

RNA

DNA

Sugar carbonshave primenumbers, todistinguish themfrom atoms inbases

Nucleotides

Deoxyribonucleotides

Ribonucleotides

Heterocyclic Nitrogen Bases

RNA DNA

DNA - POLYNUCLEOTIDE

NUCLEOTIDENUCLEOSIDE PHOSPHATE

DEOXYRIBOSE GETEROCYCLIC NITROGEN BASE

ADENIN CYTOSIN GUANIN THYMINE

RNA - POLYNUCLEOTIDE

NUCLEOTIDENUCLEOSIDE PHOSPHATE

RIBOSE GETEROCYCLIC NITROGEN BASE

ADENIN CYTOSIN GUANIN URACIL

Structure of Nucleic Acid

Only four different nucleotide bases can occur in a

nucleic acid, each nucleic acid contains millions of

bases bonded to it.

The order in which these nucleotide appear in the

nucleic is the coding for the information carried in

the molecule.

In other words, the nucleotide serve

as a sort of genetic alphabet on which the structure of each protein in our bodies is encoded.

DNA

• In the early 1950s, four scientists, James Watson and Francis Crick at Cambridge University and Maurice Wilkins and Rosalind Franklin at King's College, determined the true structure of DNA from data and X-ray pictures of the molecule that Franklin had taken. In 1953, Watson and Crick published a paper in the scientific journal Nature describing this research. Watson, Crick, Wilkins and Franklin had shown that not only is the DNA molecule double-stranded, but the two strands wrap around each other forming a coil, or helix.

WATSON-CRICK MODEL

Combination of two single strands

The Double Helix

Sugar-phosphate backbone outside,

bases inside

1953

WATSON-CRICK MODEL

Bases form specific base pairs, held together by hydrogen bonds

Structure compatible with any sequence of bases

WATSON-CRICK MODEL

The nucleotide bases of the DNA molecule form complementary pairs: adenine always bonds to thymine (and vice versa) and guanine always bonds to cytosine (and vice versa). This bonding occurs across the molecule, leading to a double-stranded system

The base pairing is the key to understanding how DNA functions

As a trick for remembering how the bases pair up (if symbols are arranged in alphabetical order):

A C G T Adenine Cytosine Guanine Thymine

Watson-Crick base pairs

Hydrogen bonds are weaker than covalent bonds (eg. C-C or C-N)Covalent bonds determine structure,Weak hydrogen bonds - Stabilize double helix

Base Pairing in DNA

DNA samples from different cells of the same species have the same proportions of the four heterocyclic bases

DNA samples from different species have different proportions of bases

Human DNA contains:

30% - Adenine equal amounts

30% - Thymine A = T

20% - Guanine equal amounts

20% - Cytosine G = C

The bases occur in pairs!!!

DNA replication

The double-stranded DNA molecule has

the unique ability that it can make exact

copies of itself, or self-replicate. When

more DNA is required by an organism

(such as during reproduction or cell

growth) the hydrogen bonds between the

nucleotide bases break and the two

single strands of DNA separate. New

complementary bases are brought in by

the cell and paired up with each of the

two separate strands, thus forming two

new, identical, double-stranded DNA

molecules.

DNA The blueprint for the structure and functioning of our bodies is contained in the genetic material found in the nucleus.

The total number of base pairs in a human cell the HUMAN GENOME is 3 billion base pairs

The genetic material (chromatin) is composed of DNA (Deoxyribonucleic acid) and protein

When a cell is not actively dividing, its nucleus is occupied by CROMATIN

25

CHROMATIN

DNA HISTONE

Chromatin is DNA wound tightly around proteins called histones. During cell division, chromatin organizes itself into CHROMOSOMES

Each chromosome contain a different DNA molecule!!!

It is a linear strand of DNA in combination with nuclear proteins

We refer to this complex of DNA and proteins as chromatin It is a linear array of genes

As a set - they are our genome

What is a chromosome?

CHROMOSOMEOrganisms differ in their number of chromosomes

64 chromosomes - 32 pairs




Heredity is encoded in DNA within the chromosomes

During cell division the DNA is duplicated so that each new cell receives a complete copy

Each DNA molecule is made up of many GENES

GENE is individual segment of DNA that contains the instructions that direct the synthesis of a single polypeptide

What is a GENE?

RNA

Ribonucleic acid, or RNA, gets its name from the

sugar group in the molecule's backbone - ribose.

Several important similarities and differences

exist between RNA and DNA.

30

DNA vs RNA

DNA consists of two associated polynucleotide strands that wind together in a helical fashion. It is often described as a double helix

Most RNA is single stranded and does not form a double helix

DNA vs RNA

DNA Composition

Deoxyribose (a pentose = sugar with 5 carbons)

Phosphoric Acid

Organic (nitrogenous) bases:

(Purines - Adenine and Guanine, or Pyrimidines -Cytosine and Thymine)

RNA Composition

Ribose (a pentose = sugar with 5 carbons)

Phosphoric Acid

Organic (nitrogenous) bases:

Purines (Adenine and Guanine) and Pyrimidines (Cytosine and Uracil)

32

DNA vs RNA

DNA Composition

The base composition is variable, but in all cases the amount of adenine is equal to the amount of thymine (A=T).

In the same manner, C=G.

Consequently

A+C = T+G

RNA Composition

The rule A+C=U+G CAN'T BE APPLIED THERE

because most RNA is single stranded and does not form a

double helix

RNA

RNA (ribonucleic acid) is the messenger of DNA within the cell.

Forms of RNA direct the cell to manufacture specific enzymes and other proteins

There are several different kinds of RNA made by the cell:• mRNA - messenger RNA• tRNA - transfer RNA• rRNA - ribosomal RNA

Central DogmaHow does the sequence of a strand of DNA correspond to the amino acid sequence of a protein? This concept is explained by the central dogma of molecular biology that deals with the detailed residue-by-residue transfer of sequential information, and states that:• information cannot be transferred back from protein

to either protein or nucleic acid.

• In other words, 'once information gets into protein, it can't flow back to nucleic acid.'

Central Dogma

Every time a cell divides, three fundamental processes known as:

• Replication• Transcription• Translation

RNA take place in the duplication, transfer, and use of genetic information

Replication

Process by which copies of DNA are made when a cell divides (each of two daughter cells has the same DNA)

Transcription

Process by which copies the genetic information in DNA is read and used to synthesize RNA

• CODON - in the mRNA is a series of three ribonucleotides that is a code for a specific amino acid.

• Example: GGU on mRNA - codon for GLYCINE

Translation

Process by which the genetic message is decoded and used to make proteins

Every cell contains 20 or

more different tRNAs, each

designed to carry a

specific amino acid.

A tRNA molecule is L-shaped

and it is a sequence of three

nucleotides called ANTICODON

• The Anticodon of each tRNA is complementary to mRNA codon

• Ex: mRNA CODON CUG

• tRNA ANTICODON GAC

Points to remember

• Nucleic Acids and their structure • Nucleotide vs Nucleoside• DNA and RNA composition• Watson-Crick model of DNA• What is a chromosome?• What is a GENE?• DNA vs RNA• Replication, Transcription, Translation

Nucleic acids

Education

Transcript of Nucleic acids