Introduction to Genetics Chapter 9: Genes & Cell Division

DNA Deoxyribonucleic acid Identified in the 20th century as the genetic material Chemical information storage Daily function, development, and reproduction of all living things

DNA as information Sequence of 4 nucleotide bases: One “word” = gene “letters” that spell amino acid sequence of proteins One “word” = gene DNA information is “read” and acted upon by other molecules (RNA, ribosomes)

DNA Backbone: (red) Bases: (blue & green) Double helix Like a spiral staircase Backbone: (red) Repeating sugars & phosphates “handrails” Bases: (blue & green) Adenine Thymine Guanine Cytosine “steps”

Genome Genome: Half comes from mom, half from dad All of an organism’s genetic information Half comes from mom, half from dad Made of DNA packaged into chromosomes

Genome is a “library” Most cells carry the organism’s complete genome Only some parts of it are in use Different genes are expressed in different cells

The “library” is packaged in volumes called chromosomes DNA is packaged The “library” is packaged in volumes called chromosomes Humans have 46 Chromatin: DNA wrapped & folded around proteins

46 chromosomes = 23 matched pairs Homologous chromosomes: A pair of chromosomes with genes for same types of proteins Homologous is NOT identical e.g., hair color Paternal: brown Maternal: black

Karyotype

Cell Division to grow to replace dying cells to adapt to changing needs Uncontrolled cell division = CANCER

Cell Division Cell can’t just break in half Must replicate the genome and precisely distribute it so each daughter cell gets the whole “library”

DNA replication Mitosis Cytokinesis

The Cell Cycle

Phases of the Cell Cycle G1: normal cell life S: DNA synthesis/replication G2: preparation for cell division M (mitosis): division of the chromosomes G0: cells that don’t divide

one nucleotide at a time S phase Original DNA unwinds; acts as template for replication New strands are synthesized, one nucleotide at a time

Chromatids Chromatin changes appearance: Individual chromosomes are visible only after duplication (DNA replication) Chromatids

Telophase & cytokinesis Phases of Mitosis M G1 S G2 Prophase Metaphase Anaphase Telophase & cytokinesis

Mitosis: Prophase Chromatin condenses Nuclear envelope breaks down Centrosomes: microtubule organizing centers

Mitosis: Metaphase Microtubules from the centrosomes form mitotic spindle Microtubules attach to chromosomes and align them at “equator”

Mitosis: Anaphase The genome divides! Sister chromatids are pulled apart

Mitosis: Telophase & Cytokinesis Nuclear membranes re-form Chromosomes lose shape Cytoplasm is split in half

Cell Division in Plant Cells Only difference: cell can’t pinch in half

Prokaryotes: Binary Fission No nucleus, only one chromosome