2Structure of DNA Deoxyribonucleic Acid DNA is one of the two nucleic acidsDNARNAIt is composed of repeating subunits (monomers) called NUCLEOTIDES.A nucleotide has three components– deoxyribose sugarA phosphateA nitrogenous base
3Nitrogenous Bases Adenine (A) Guanine (G) Cytosine (C) Thymine (T) These are grouped intoPurines – two carbon rings (A and G)Pyrimidines – one carbon ring (T and C)
4The Double HelixA always pairs with TC always pairs with G
5DNA Replication1. Helicase enzymes cause the strands to unwind and separate. (The point where the two chains separate is the replication fork.)2. DNA polymerases bind to each chain of DNA.3. The DNA polymerase moves along the chain and aids in the addition of nucleotides for the formation of the new chain.
6DNA replication does not begin at one end of the molecule and proceed to the other end. DNA replication occurs in many points simultaneously along the molecule.
7Accuracy and RepairDNA replication is very accurate – about 1 error in every 10,000 paired nucleotides.DNA has the ability to proofread and repair mistakes.An error in replication is known as a MUTATION.DNA may also be damaged by a variety of agents which include chemicals and ultraviolet light.
8What is an enzyme? An enzyme is a catalyst that is usually an protein. Enzymes are substrate specific.They have a lock and key fit.Allow reaction in living organisms to occur at lower temperatures by reducing the activation energy.Usually end in –ase and identify the substrate the work on. Example: proteases, nucleases
9Chromosomes are Composed of DNA DNA in humans is about 6 billion pairs of nucleotides and is located in the nucleus as chromosomes.Each chromosome is a single DNA molecule associated with protein.DNA in eukaryotes wraps tightly around proteins called HISTONES.A chromosome consists of two identical halves called chromatids.
11The consticted area of each chromosome is called a chromatid (a protein disk), Between cell divisions, the DNA is not so tightly wound and is called chromatin.Centromerechromatid
12Each species has a characteristic number of chromosomes – see pate 146. Human and animal chromosomes are categorized as sex chromosomes or autosomes.Sex chromosomes determine the sex of the organismAutosomes are all other chromosomesEvery cell has two copies of autosomes. These copies are called homologous chromosomes
13HOMOLOGOUS CHROMOSOMES SAME SIZESAME SHAPESAME GENES FOR THE SAME TRAITSHomologous chromosomes may be arranged in order to form a karyotype.
15Diploid – having two sets of chromosomes Both chromosomes of the homologous pairBoth of the sex chromosomesHaploid – having only one set of chromosomesHalf of the chromosome numberOne chromosome of the homologous pairOnly one sex chromosome
16Cell Division Eukaryotes Prokaryote Membrane bound organelles DNA is in chromosomesTwo processes for cell divisionMitosisMeiosisProkaryoteNo membrane bound organellesOnly one circular chromosomeReproduce by binary fission