DNA Structure & the Genome Bio160 General Biology
Lecture Outline I. DNA A nucleic acid II. Chromosome Structure III. Chromosomes and Genes IV. DNA vs. RNA
I. DNA A Nucleic Acid Structure of DNA: Remember: DNA & RNA are nucleic acids, polymers of nucleotides nucleotide structure Classification of Nucleotides 1. Pyrimidines single ring base Cytosine Thymine Uracil 2. Purines double ring base Guanine Adenine
I. DNA A Nucleic Acid Creating a Nucleic Acid (polymerization) Nucleotide monomers are joined together by: dehydration synthesis creates a phosphodiester bond the 3 rd carbon and the 5 th carbon of the ribose are involved dehydration synthesis
I. DNA A Nucleic Acid Nucleotide polymerization creates one strand of the double helix the complimentary strand is then created using the primary strand as a model adenine always pairs with thymine guanine always pairs with cytosine two strands are held together by hydrogen bonds between the complimentary bases
I. DNA A Nucleic Acid Why do we care about the sequence of nucleotides? 1. It is what creates the genome! It s the unique arrangement or sequence of nucleotides: in prokaryotic organisms the genome exists on a single loop of double stranded DNA within an area called the nucleoid region. in eukaryotic organisms the genome exists on multiple double stranded and linear DNA segments called chromosomes
II. Chromosome Structure A Chromosome is the highly condensed form of DNA it takes this form during cell division The number of chromosomes varies between species, the number of chromosomes is designated by (n). AND Different species have different copies of each chromosome, the number of copies is designated by a number in front of (n). for example: Humans, n = 23, but as we have two copies of each chromosome we are designated 2n or diploid and therefore have 46 chromosomes in each of our somatic (non-gamete producing) cells. 1. chromatid 2. centromere 3. short arm 4. long arm
II. Chromosome to Chromatin In order to access the information imbedded in the sequence of nucleotides the DNA is usually in a loosely compacted state called chromatin To ease the process of cell division, the chromatin condenses even further to create a chromatid chromatids are replicated during part of the cell cycle to create the familiar chromosome this should be technically called a replicated chromosome.
III. Chromosomes & Genes A gene is a specific sequence of nucleotides at a specific location (locus) that contain in their sequence the necessary information to encode a functional RNA product. The RNA product then contains the necessary information to make a protein!
III. Chromosomes & Genes Because organisms typically have more than one copy of a chromosome and each chromosome contains our genes at a very specific locus we have at least two copies of a gene, each which may be slightly different because one copy came from mom, the other from dad These copies of a gene are called alleles and the expression of these make up an organisms traits. The expression of traits is called an organisms phenotype The make-up of the gene is called an organisms genotype
IV. DNA vs. RNA DNA exists as a double helix with antiparallel strands uses the sugar deoxyribose long strands uses four base pairs guanine & cytosine adenine & thymine RNA exists transiently as a single strand uses the sugar ribose relatively short strands uses four base pairs guanine & cytosine adenine & uracil
IV. DNA vs. RNA DNA contains the entire genome unique to each individual common to a population no individual can have a gene that does not exist within the gene pool... unless - MUTATION RNA has different forms mrna & trna are used in protein production rrna used in ribosome production ribosomes are then used in protein production So what does all this DNA control? Everything we ll start with the cell cycle next time!