DNA RNA BIO

3.1.5.1 DNA-DEOXYRIBONUCLEIC ACID

• Dna is the material of heredity , it stores genetic information.
• Consists of: 2 POLYNUCLEOTIDE STRANDS arranged into a double helix.
• The 2 strands=arranged in an anti-parallel formation, running in opposite directions relative to each other.
• A gene contains the instructions for making 1 polypeptide.
• The DNA code is a TRIPLET CODE, so 3 bases code for 1 amino acid.
• ALWAYS REFER TO THE TEMPLATE STRAND AS :
• "THE TEMPLATE STRAND THAT CODES FOR 1 POLYPEPTIDE."
• Base Pair rule: Adenine bonds to Thymine, Cytosine bonds to Guanine.
• Nucleotide is made of: Deoxyribose (Dna of pentose sugar), phosphate group, organic base.
• CHARGAFF's DATA:
• -General ratio of bases- 1:1
• -what tells about how Nucleotides join to one another?
• A bonds to T and C bonds to G.
• -If ratio not 1:1, may have a single strand of DNA.

Slide 2

• NUCLEOTIDES
• Polynucleotide strand =made up of nucleotides (millions of monomers).
• Each nucleotide consists of :
• Phosphate Group
• Nitrogenous Base
• Pentose Sugar.
• There are 4 organic bases, the alphabet of GENETIC DIVERSITY for all organisms on Earth is therefore written in just 4 letters.
• 2 Types:
• 1.) Single Ring Bases(PYRIMIDINES)
• -Cytosine
• -Thymine
• 2.) Double Ring Bases (PURINES)
• -Adenine
• -Guanine.
• The parts in a nucleotide are joined to one another by condensation reactions and form strong COVALENT BONDS.
• Each base will only bond with 1 other specific base.
• A,T form a base pair. 2 H BONDS BETWEEN A and T.
• C,G form a base pair. 3 H BONDS BETWEEN C and G.
• Nucleotides are joined to one another by condensation reactions, forming a phosphodiester bond.
• The bases project inwards, held together by WEAK HYDROGEN BONDS.

Slide 3

• 1.)
• QUESTION: WHY IS DNA suitable as the molecule of inheritance?
• Answer: VERY STABLE molecule. Since there are 3 H bonds between C and G, the more C-G pairings there are, the more stable the DNA.
• 2.)
• H bonds make polynucleotide chains easy to separate during protein synthesis.
• 3.)
• V. Large molecule, capable of carrying a large amount of info.
• 4.)
• The base pairs=given some protection against CORRUPTION by being in the centre of the double helix structure.
• 5.)
• Phosphodiester bonds between nucleotides in a polynucleotide strand are VERY STRONG.
• 6.) QUESTION: How does DNA determine an organisms characteristics?
• ANSWER: DNA bases make up a TRIPLET CODE, which determines the order of amino acids in a protein (primary structure).
• A gene is the instructions for making a polypeptide.
• Polypeptides combine to form proteins.
• Proteins can:
• 1.) Have structural roles.
• 2.)Be Hormones.
• 3.) Be enzymes.
• Therefore proteins control the chemical reactions that are responsible for growth, development, and day-to-day functions within an organism

WHAT IS IN DNA?

• GENES- Instructions for making polypeptides.
• START+ STOP CODONS- Found at start and end of genes and are important when genes are copied.
• Introns- Sections of DNA found in genes that are removed prior to polypeptide production and that do not code for amino acids.
• Exons- sections of DNA in genes that code for amino acids.
• Junk DNA- Some large areas of DNA that separate genes but do not themselves code for anything. (This is not actually junk- it contains genetic evolutionary history and promotor sequences that indicates DNA copying in eukaryotes.)
• RNA:
• -Single stranded
• -opp of DNA
• -small
• -T replaced by U
• -Deoxyribose replaced by Ribose.
• MessengerRNA- Acts as an INTERMEDIARY MOLECULE during protein synthesis , COPYING the genetic info in DNA during TRANSCRIPTION and conveying that info to the RIBOSOME. (Found between ribosomes and nucleus).
• TransferRNA- DECODES the MRNA sequence into a protein during TRANSLATION.
• Each type of TRNA carries a specific AMINO ACID.
• (Carries amino acids to ribosomes).
• RibosomalRNA- The DNA component of the ribosome which is essential for PROTEIN SYNTHESIS in all living organisms.

MECHANISM OF DNA REPLICATION!

• 1.) Replication starts at (a specific sequence on the DNA molecule called) the replication origin.
• 2.) Enzyme DNA HELICASE unwinds and separates the 2 strands of DNA, breaking the H bonds between the base pairs.
• The helix unwinds to form 2 single strands.
• 3.) Each original strand acts as a template for a new strand. COMPLEMENTARY BASE PAIRING means that the free-floating DNA nucleotides are attracted to their complementary bases on each original template strand.
• 4.) CONDENSATION REACTIONS join the nucleotides of the new strand together- catalysed by the enzyme DNA POLYMERASE- H bonds form between bases on the original and new strands.
• Each new DNA molecule contains on strand from the original DNA molecule and one new strand.
• 1.) REPLICATION ORIGIN.
• 2.)DNA HELICASE ... BREAKING H BONDS
• 3.)COMPLEMENTARY BASE PAIRING
• 4.)CONDENSATION REACTIONS
• DNA POLYMERASE
• 5.)EACH NEW DNA MOL -1 STRAND OG MOL, 1 NEW STRAND.

DNA REPLICATION

• IS THE PROCESS OF DUPLICATION OF THE ENTIRE GENOME PRIOR TO CELL DIVISION
• Method=semi-conservative replication where 1/2 of the strands in each new DNA mol= from the OG DNA mol.
• Therefore there is genetic continuity between generations of cells (cells produced from cell division inherit their genes from parent cells.)
• Extreme accuracy of DNA replication=necessary in order to preserve the integrity of the genome in successive generations.
• DNA=copied/replicated before every cell division, so that one identical copy can go to each daughter cell.
• Semi conservative replication
• Each new double stranded daughter piece of DNA formed has one polynucleotide strand from the original parent double helix.
• Conservative replication
• The parental double helix remains intact: both strands of the daughter double helix are newly synthesized.