DNA The DNA molecule model was proposed by James Watson and Francis Crick.
Double Helix Complementary Base Pairing: certain bases always pair with each other A with T G with C
DNA Replication Replication of DNA: DNA unwinds and Helicase (enzyme) breaks apart the 2 strands. Each strand serves as a template for the new DNA
DNA Replication DNA polymerase: (enzyme) that adds nucleotides to each strand of DNA. Many polymerases attach at the same time. On a fruit fly DNA replication starts at 6,000 different places
DNA Replication According to the base pairing rules, what would the new stand of DNA be if the original strand was A – T – T – C – C- G
DNA Replication Accuracy and Repair DNA is copied with a high degree of accuracy Mutation: change in the nucleotide sequence of DNA; it can have serious effects on the organism. Can be harmful or beneficial
DNA Replication Environmental factors can damage DNA Ex. Ultraviolet radiation from the sun, enzymes work to repair the damaged DNA What do you think would happen if the repair enzymes weren’t working properly?
Cell Division Now you know what DNA is…… how does the cell organize DNA for Mitosis.
Cell Division Chromosomes – tightly coiled Strands of DNA wrap packages of DNA; they are rod around proteins called shaped and proteins hold them Histones. together.
Cell Division Chromatid – half of a chromosome; forms as DNA copies itself before cell division Centromere – holds the chromatids together until they separate
Important Words How many chromosomes do humans have? Each species has a unique number of chromosomes. 46 chromosomes or 23 pairs.
Types of Chromosomes 2 Types of Chromosomes: 1. Sex Chromosomes – are the chromosomes that determine the sex of an organism. Female: XX Male: XY 2. Autosomes – all other chromosomes Humans: 44 autosomal chromosomes
Chromosomes Homologous chromosomes – two copies of each autosome (maternal and paternal) Homologous chromosomes are the same size, shape, and carry genes for the same trait.
Chromosomes Karyotype – is a picture of the chromosomes in a dividing cell. 22 homologous pairs of autosomes. 2 sex chromosomes
Chromosomes Diploid (2n)– cells have two sets (maternal and paternal) of chromosomes. Has all 46 chromosomes. Haploid (n)– cells have one set of chromosomes. Has 23 chromosomes. Gametes
Chromosomes Examples of haploid cells? Gametes - sperm and egg cells; they have 23 chromosomes Fertilization 23 in sperm + 23 in egg = 46
Cell Division Where do new cells come from? All cells came from preexisting cells. Why do cells divide? 1. Increase Cell volume 2. Growth 3. Repair tissue and organs 4. Reproduce
Cell Division Prokaryotes – cell division by: Binary Fission DNA copied, cell grows, cell splits in two. Eukaryotes – cell division by 2 ways: Mitosis new cells have identical genetic material; produces clones. Meiosis reduces chromosome number in half, makes sex cells (gametes).
Cell Cycle The Cell Cycle – a repeating set of events that make up the life of a cell. There are 3 steps to the cell cycle.
Cell Cycle 1. Interphase – the longest phase, in between cell division G1 phase – growth of cell G0 phase – inactive stage. S phase – DNA is copied (“S” synthesis of DNA) G2 phase – growth of cell; prepares for cell division *G0 phase – non dividing state after the G1 phase; Ex. Many cells in human body – nervous system cells
Mitosis 2. Mitosis – division of the nucleus; a continuous process divided into 4 phases 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 3. Cytokinesis – division of the cytoplasm The chromosomes start to uncoil and become less dense Two new, identical cells are formed