Transcript CHROMOSOMES
CHROMOSOMES 8-1 http://web.jjay.cuny.edu/~acarpi/NSC/12-dna.htm DNA Found in NUCLEUS Carries the genetic code http://encarta.msn.com/media_461516495/Nucleus_of_a_Cell.html NUCLEIC ACIDS are built from subunits called ____________________ Image by: Riedell Changing the sugar _____________ and _______________ nitrogen base produces different subunits 5 NITROGEN BASES _____________= ADENINE A _____________ GUANINE = G _____________ CYTOSINE = C ______________ THYMINE = T (only in DNA) ______________= U (only in RNA) URACIL DNA molecule forms a HELIX or “twisted ladder” A on one strand always bonds with T opposite it G on one strand always bonds with C opposite it Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif DNA CAN BE: SPREAD OUT IN NON-DIVIDING CELLS SCRUNCHED UP IN DIVIDING CELLS PROTEINS that wrap up DNA are called __________________ http://biology.kenyon.edu/courses/biol114/Chap01/chrom_struct.html PROTEINS ProteinsCombine with DNA to make chromosomes Image from: http://employees.csbsju.edu/hjakubowski/classes/ch331/dna/chromosome.gif Proteins that control the activity of genes are called ________________ http://www.blc.arizona.edu/courses/181summer/14.html Cells turn genes on or off as needed (part of differentiation) Example: Genes for making digestive enzymes are turned off in brain cells Genes for making neurotransmitters are turned on NON-HISTONES are the “on-off” switches for genes CELL DIVISION GENES Some cells divide frequently (some human skin cells divide once/hour) Some cells divide occasionally (liver cells divide about once/year) Some cells don’t divide once they form (nerve cells) Cancer cells have lost control of their cell division genes Cancer cells • Don’t stop dividing • Like a “car with no brakes” • Can spread to new places (METASTASIS) • ______________ are substances that can damage DNA Ex: Radiation, cigarette smoke, chemicals in environment DNA in PROKARYOTES • BACTERIAL DNA is CIRCULAR • HAVE ONE CHROMOSOME • ATTACHED TO CELL MEMBRANE http://www.origin-life.gr.jp/3202/3202121/fig6.jpg DNA in EUKARYOTES (Plants & Animals) • DNA is ROD-SHAPED CHROMOSOMES • MANY PAIRS • FOUND IN NUCLEUS http://cellbio.utmb.edu/cellbio/chrom2.jpg Chromosome structure • ___________________ 2 identical arms • __________________ constricted area holds chromatids together •__________________ PAIR 2 of each chromosome (one from mom; one from dad) HOMOLOGOUS CHROMOSOMES • SAME SIZE • SAME SHAPE • CARRY GENES for the SAME TRAITS (Don’t have to have the SAME CHOICES) http://arnica.csustan.edu/biol3020/cell_division/cell_division.htm CHROMOSOME NUMBERS • Each species has a characteristic number of chromosomes • HUMANS have 46 chromosomes (23 pairs) You can’t judge a critter by its chromosomes This critter has 54 chromosomes Corn has 10 pair of chromosomes Snails have 18 pairs of chromosomes A mouse has 40 chromosomes CHROMOSOME NUMBER DOESN’T CORRESPOND TO SIZE OF ORGANISM Big animals DON’T have more chromosomes than small animals! http://www.ocean.udel.edu/extreme2004/genomics/images/chromosomes.gif • Chromosomes that determine the sex of an organism = _________________________ • All other chromosomes = _________________ Humans have two sex chromosomes And _____ autosomes A _____________is a picture of an organism’s chromosomes A KARYOTYPE can tell the sex of an organism In humans XY is a male In humans XX is a female Guess who? XY Karyotypes can also show some genetic problems http://members.tripod.com/~yenial/chromosome.html Eric has Down’s Syndrome 1 in 750 births Has extra #21 chromosome Mental retardation DIPLOID & HAPLOID Some cells have 2 copies of each chromosome = _______________ (one from mom; one from dad) • All BODY cells are diploid Image from: http://www.ncu.edu.tw/~ls/graph/faculty_pictures/whole_time/SLC/SLC_lab-1.jpg DIPLOID & HAPLOID Some cells have only one copy of each chromosome = ____________________ All sperm and egg cells are haploid http://www.angelbabygifts.com/ EGG + SPERM If egg and sperm had same number of chromosomes as other body cells …. baby would have too many chromosomes! CELL DIVISION 8-2 Mitosis and Meiosis CELL DIVISION in PROKARYOTES Bacteria reproduce using __________________ •DNA is copied •Cell wall forms •Cell splits into two new cells http://www.tnau.ac.in/notesbscag/agm/UGMicro/AGM151_201/theory_files/image156.jpg CELL DIVISION IN EUKARYOTES __________ OR __________ MITOSIS • Makes ____ cells identical to parent cell • Makes _____ cells • Makes _______ cells • Used to _____________ & _________________ ___________________ MEIOSIS • Makes ____ cells with different DNA • Makes _____ cells • Makes ____________ • Used ______________ CELL CYCLE G0 CELL CYCLE cells alive cell cycle CELL CYCLE INTERPHASE – non dividing phase G1- Grow bigger Cell is “doing its job” DNA is spread out as chromatin S - Synthesis (copy DNA) G2- Grow bigger, make organelles & molecules needed for cell division CELL CYCLE MITOSIS – Cell division Prophase Metaphase Anaphase Telophase Cytokinesis G0 – cell stops dividing (Ex: nerve cell) INTERPHASE (G1 - S - G2) In between divisions Cells are in this phase most of the time Can see nucleus DNA spread out as chromatin Can’t see chromosomes DNA gets copied Cell gets ready to divide PROPHASE 1st dividing phase DNA scrunches into chromosomes Nuclear membrane & nucleolus disappear Centrosomes containing centrioles appear & move to poles Spindle fibers form & attach chromosomes METAPHASE Chromosomes line up in ___________ ANAPHASE Centrioles pull chromosomes ________ TELOPHASE (reverse prophase steps) See ______ nuclei Nuclear membrane & nucleolus return Chromosomes spread out as chromatin Centrioles disappear Spindle fibers disappear CYTOKINESIS Cytoplasm splits into 2 cells ANIMAL CELLS pinch cytoplasm in two with a ______________________ CYTOKINESIS Cytoplasm splits into 2 cells PLANT CELLS can’t pinch because they have a ______________ Separate cytoplasm by growing a _________________ down the middle. CELL CYCLE G0