Nucleic Acids DNA 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 carbons have prime numbers, to distinguish them from atoms in bases

Nucleotides Deoxyribonucleotides Ribonucleotides

Heterocyclic Nitrogen Bases RNA DNA

DNA - POLYNUCLEOTIDE NUCLEOTIDE NUCLEOSIDE PHOSPHATE DEOXYRIBOSE GETEROCYCLIC NITROGEN BASE ADENIN CYTOSIN GUANIN THYMINE

RNA - POLYNUCLEOTIDE NUCLEOTIDE NUCLEOSIDE 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% - CytosineG = 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?

CHROMOSOME Organisms differ in their number of chromosomes 64 chromosomes - 32 pairs 38 chromosomes - 19 pairs 6 chromosomes - 3 pairs 46 chromosomes - 23 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 Dogma How 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