Genome, Karyotype and Chromosome Disorders

• Genome refers to the complete set of genetic instructions found in an organism.
• A karyotype is a display of an organism's complete set of chromosomes, arranged in pairs by size and type.
• Autosomes are non-sex chromosomes.
• Sex chromosomes determine an individual's sex (XX for females, XY for males).

Karyotype Creation

• Chromosomes photographed during meiosis are cut out.
• These chromosomes are then grouped in pairs and arranged in order of decreasing size.
• A male karyotype is denoted as 46 XY, while a female is 46 XX.

Nondisjunction

• Nondisjunction occurs when problems with the meiotic spindle cause errors in daughter cells.
• Trisomic cells have three copies of a chromosome, resulting in a 2n+1 total chromosome number.
• Monosomic cells have only one copy of a particular chromosome.
• Polyploidy is when organisms have more than two complete sets of chromosomes, common in plants but uncommon in animals.

Sex Chromosome Disorders

• Klinefelter's Syndrome: XXY male, occurring in 1 in every 2000 live births, results in sterile males.
• Turner's Syndrome: XO Female, occurring in 1 in every 5000 births, produces phenotypic but immature females.

Genetic Material

Transformation of Bacteria

• In 1928, Griffith's experiments with Streptococcus pneumoniae showed transformation.
• S strain bacteria (smooth colonies): Harmful.
• R strain bacteria (rough colonies): Harmless.
• Heat-killed S strain mixed with live R strain killed mice, suggesting genetic transformation.
• Heating the S Bacteria denatured its proteins and enzymes, but the DNA was unaffected.
• Transformation: One strain of bacteria is changed by a gene or genes from another strain of bacteria.
• Oswald Avery (1944) aimed to identify the molecule carrying genetic information.
• Avery used organic chemistry to selectively remove molecules to see what molecule cannot be absent for the transformation.

What is a Virus?

• A virus is a tiny, simple, nonliving particle composed of protein and nucleic acids (DNA or RNA).
• Viruses can only be seen with powerful electron microscopes.

Viral Structure

• Capsid: A protein coat that protects the DNA and RNA, instructing the host to produce more viruses.
• Viruses come in various shapes: crystals, spheres, cylinders, spacecraft.
• Viruses are not alive because they can't reproduce on their own.

Hershey and Chase Experiment

• Bacteriophages (viruses) were tagged with radioactive isotopes: P32 for DNA and S35 for protein.
• Radioactivity was found in the DNA, confirming DNA as the genetic material.
• These results supported Avery's findings.
• DNA is the genetic material found in genes and is the base for all living things.

DNA Structure

• Nucleotide: monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
• Purines (double ring): Adenine and Guanine.
• Pyrimidines (single ring): Cytosine and Thymine.
• Adenine and Thymine make up 20% each, and guanine and cytosine make up 30% each.
• Chargaff's Rule: The amount of cytosine equals the amount of guanine, and the amount of adenine equals the amount of thymine.

Discovering the Model

• Rosalind Franklin used X-ray diffraction to discover the model of DNA.
• Franklin's Photo 51, was used by Watson and Crick to discover the double helix structure.
• Watson and Crick built a 3D model of DNA using Franklin's findings.
• The double helix structure of DNA features hydrogen bonds (three between G and C, two between A and T).
• The sugar-phosphate backbone provides a rigid structure.

DNA to Chromosomes

• Chromatin: Less condensed DNA, tightly coiled around proteins within the nucleus.
• Chromosomes: Condensed chromatin.
• Histone: The protein around which DNA is coiled.
• Prokaryotic DNA lacks a nucleus and typically has one circular chromosome in the cytoplasm, along with plasmids.
• Eukaryotic DNA has 1000 times more base pairs than bacterial DNA.
• A Eukaryotic smallest human chromosome has 30 million base pairs.

DNA Replication

• DNA replication is a semi-conservative process which helps the strand replication.

Steps of Replication

• Enzymes unwind and "unzip" the double helix.
• DNA polymerase attaches corresponding nitrogenous bases.
• Each old strand serves as a template for a new strand.
• New helices re-wind.
• Complementary Base Pairing: DNA separates into two strands, producing two new complementary strands following base pairing rules.
• DNA's Structure: Antiparallel Strands
• Two DNA strands run in opposite directions (antiparallel).
• Nitrogenous bases connect at the center.
• Topoisomerases help with supercoiling/winding.
• Helicases unzip the DNA.
• Single-strand binding proteins cap the original strand.
• Primases create RNA primers.
• DNA polymerases synthesize new strands.
• Ligases join DNA fragments.
• DNA polymerase later replaces the primer with deoxyribonucleotides complementary to the template

Telomeres:

• Telomeres are repetitive sequences at the ends of eukaryotic chromosomes that do not code for genes
• Telomerase: An enzyme which reforms shortening telomeres.
• Active in stem cells and cancer. (Turned off in adult cells)

Replication Errors:

• Gene: A segment of DNA with a particular sequence of bases (ATGC). Genetic Mutation happens when a change occurs to this sequence
• Some mutations are due to errors in DNA replication and these are prevented by proofreading enzymes.

Environmental causes of DNA Damage:

• UV radiation in sunlight
• Chemicals in tobacco smoke
• Nuclear radiation
• Pesticides
• Pollutants
• DNA repair enzymes fix most DNA damage.
• Genetic mutations can be harmful, beneficial, or have no effect.
• Mismatched DNA Repair: Special enzymes fix incorrectly paired nucleotides.
• Nucleotide excision repair: Nuclease cuts out damaged strand segments.
• DNA Polymerase and Ligase are also used for DNA repair.

RNA and Protein Synthesis

• Relate the central dogma of molecular biology to protein synthesis.
• Describe the process of transcription and translation.
• Central Dogma of Molecular Biology: DNA to RNA to PROTEIN
• Gene expression is the process of proteins putting genetic information into action in living cells

Mismatched DNA Repair

• In Mismatch repair, special enzymes fix incorrectly paired nucleotides
• In nucleotide excision repair nuclease cuts out a segment of a damaged strand’
• DNA Polymerase
• Ligase
• RNA and Protein Synthesis

Comparing DNA and RNA

• Genes and Proteins 1 Amino Acid = 3 nucleotide bases
• Polypeptide = Amino Acid Chain Protein = 1 or more Polypeptides
• Proteins and Traits Proteins are chemical triggers for many cell functions
• Proteins determine traits GENE:
• Segment of DNA that specifies the amino acid sequence of a protein
• RNA serves as a temporary copy of DNA that translates this code into a protein
• Two Major Parts of Protein Synthesis
• Transcription which Occurs in the Nucleus and is the Formation of a single strand of messenger RNA from DNA in the nucleus.
• Translation Occurs on ribosomes (cytoplasm) when the Cell uses the information on mRNA to assemble amino acids in the proper order to form specific proteins
• Types of RNA: Messenger RNA Transfer RNA Ribosomal RNA

Transcription:

Occurs in nucleus RNA Polymerase Unwinds DNA and Breaks Hydrogen Bonds Then binds to promoter sequence on DNA RNA Polymerase transcribes a single strand of mRNA mRNA Editing - Intron & Exon Intron is an Intervening sequence of DNA that does not code for a protein Exon is an Expressed sequence of DNA used for protein coding.

The Genetic Code (mRNA)

Based on the four bases of mRNA (A,G,C,U) Words are 3 RNA sequences and have a Start and Stop Codons Methionine AUG us the start codon There are 3 different stop codons mRNA is transcribed in the nucleus and enters the cytoplasm for translation.

Mutations

• Mutation is a Change in a DNA sequence that affects genetic information
• Mutagen is a mutation causing agent
• Gene mutation is a Mutation in a single gene and a Chromosomal Mutation is a Mutation that changes an entire chromosome
• A Point Mutation (substitution) mutation that affects a single nucleotide, usually by substituting one nucleotide for another(Inversion)
• A Frameshift Mutation (insertion or deletion) is known as a mutation that shifts the “reading” frame of the genetic message by inserting or deleting a nucleotide.
• Types of Mutations happen as either Silent, Missense, or Nonsense

Changes in Chromosome Structure

• Deletion: A chromosome fragment lacking a centromere is lost during cell division
• Duplication: A fragment becomes attached as an extra segment to a sister chromatid.
• Chromosomal Mutation
• Inversion: A chromosomal fragment reattaches to the original chromosome in the reverse orientation Translocation: A chromosomal fragment joins a nonhomologous chromosome
• There are two ways in which DNA can become mutated: Mutations can be inherited from Parent to child or Mutations can be acquired via Environmental agents (mutagens) like Pesticides, Tobacco, UV radiation or Nuclear radiation and even Mistakes when DNA is copied Retro Virus: RNA based Virus

Lactose

• When lactose is absent, the regulator gene codes for a repressor that binds to the operator and prevents RNA polymerase from binding to the promoter, therefore Transcription for the enzymes needed to digest lactose does not take place.
• When lactose is present, the lactose molecules bind to the repressor, changing the shape of the repressor, therefore The repressor molecule cannot bind to the operator, meaning RNA polymerase CAN bind to the promoter and transcription does take place
• Gene Regulation: The enzymes needed to digest lactose are created unnecessary to waste Prokaryotic Gene Regulation
• Will often have one OPERATOR (regulatory site) controlling the expression of more than one gene, which is known as OPERON
• Eukaryotic Gene Regulation: Eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon.