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The authors of thr book Biology for a Changing World SECOND EDITION Probably dislike me lumping CHAPTERS 9 & part of 11 Mitosis & Meiosis
Stuff you’ll probably want to know Stages of mitosis and when it happens What is cancer? How is making gametes (sex cells) different from making normal cells? How is sex determined in humans? In other animals
Cell Division – 2 ½ types 1. Meiosis – eukaryotes make cells for sex In humans, “eggs” or “sperm” will discuss in detail later Half the DNA of normal cells 2. Mitosis – eukaryotes make any other cells ½ “binary fission” – prokaryote division Basically like mitosis, but we gave it special name
Mitosis & Binary Fission “Mitosis” – how eukaryotes make normal cells New cells for growth New cells for replacement of old/damaged cells Asexual reproduction Term often misused, even by biologists!!! mitosis = nucleus cytokinesis=division of rest of cell “Binary Fission” – how prokaryotes reproduce
Cell Division - Terms to know • “parent cell” – one that will divide • “daughter cell” – created by cell division • One parent forms two daughters Equal division (daughters are identical)
1 Parent 2 Daughter
Mitosis – eukaryote’s normal cell division • Eukaryotes – equal DNA in each daughter • One normal cell adult human (or any other organism) • Replacement cells RBC wear out Stomach cells eaten by acid Skin cells worn away
Mitosis: 3 reasons Development/growth Cell replacement Wound healing
Mitosis – asexual reproduction • Many single-celled eukaryotes • Some multicellular eukaryotes Example: fungi, seaweed, and sponges • DO NOT ASK (yet)
Eukaryotes – “mitotic division” • Mitotic division – 1 parent 2 daughter cells Each daughter identical to parent Same DNA as parent • Two processes in mitotic division Mitosis – dividing the nucleus Cytokinesis – dividing the rest of the cell
Prokaryotes – binary fission • Prokaryote cell repro “binary fission” • Same idea as mitosis • No nucleus to divide
Mitosis – DNA In Daughter Cells • Same DNA as each other • Same amount as parent originally had • How? – Double the DNA, then Divide • When? – Before mitosis – “INTERPHASE”
Both mitosis and binary fission • Mitosis - “Double the DNA, then divide” • Parent starts with normal • Parent DOUBLES the dna • Parent divides 1 parent 2 daughter cells • Each daughter has normal amount of DNA
How do cells divide? • cell does not simply split in half • pass through a series of phases Cell cycle • ordered sequence of stages • preparatory and division phases • one cell to two identical cells
Interphase – when we double • “Interphase” = time between divisions most of the time is spent in interphase • Doubling of DNA happens during interphase • More details later
How do cells divide? Division phase • mitosis • cytokinesis
The Cell Cycle • The cell cycle = new cell dividing cell • 90 minutes to 24 hours, varies with cell type • Two main stages Interphase Mitosis (cell division)
Cell Cycle – 2 main stages • Interphase: – Does normal cell stuff • Nutrients in, makes proteins, special functions – Grows – Gets ready to divide (includes “double the DNA”) • Mitosis (divides): – Physical division of the cell – Production of two daughter cells
How do cells divide? Preparatory phase • copy cellular contents • duplicate organelles, DNA, and cytoplasm • each new cell has the same amount as original cell • interphase • G 1, S, G 2
Interphase – three parts • Interphase = G 1, S, and G 2 – G 1 = Grow – S = “Synthesis” – G 2 = Grow some more
How do cells divide? Interphase G 1 phase • cell grows, makes cytoplasm S phase • DNA replication, chromosomes • identical sister chromatids G 2 phase • cell prepares for division
Most Cells in Adult Don’t Divide • Most adult cells enter a nondividing phase called G 0 • The G 0 phase can last from a few days to the lifetime of the organism
Proteins regulate growth & division • Cells divide when signaled (internal or external) • Humans have cell cycle regulatory proteins • Can start division or stop/pause it Checkpoint = regulatory protein
Cell division is tightly regulated Mutation occurs Cell cycle checkpoints • either repair damage OR • direct cell to commit suicide (apoptosis)
Cancer: when checkpoints fail If there’s enough DNA damage to interfere with multiple checkpoints: • cancer: cells divide uncontrollably • tumor may form
Cancer Kills by – crowding out normal cells – invading other organs – secreting poisonous chemicals
OK, back to happy topics Doubling the DNA (S part of interphase) • Chromosomes • Doubled chromosomes • chromatids
Chromosomes “chromatin” = DNA wrapped around histone proteins Chromatin is packed into chromosomes
Normal doubled Normal chromosomes have one strand Doubled chromosomes have two strands
Centromere • DNA is doubled during S phase – Two identical copies, hooked together at “centro. Mere” – “sister chromatids” – Will separate and put one chromatid in each daughter cell Do not confuse with Centrosome or centriole In the cytoplasm
Replicated chromosomes & chromatids Mitosis = dividing the DNA • chromosomes are evenly divided • sister chromatids are separated • Centromere • One doubled chromosome (two chromatids) becomes two chromosomes
Chromosomes & chromatids Before division: • doubled chromosome – Each ½ is a “chromatid” – Each ½ of doubled has normal amount of DNA • Anaphase: pulled apart Doubled chromosome 2 normal chromosomes (one for each daughter cell) After Division • “Chromosome” = normal chromosome – What used to be called “chromatid”
Most Human Cells Have Two Copies of Each Type of Chromosome • two copies of each chromosome – homologous pairs • Humans: 46 chromosomes (23 pairs) • One set of chromosomes, called sex chromosomes, determines the sex of an individual animal
Karyotype – picture of chromosomes • Different species have different chromosome # • “karyotype” = Picture of all the chromosomes in normal cell • “Homologous” pairs
Cell Cycle • Interphase – growing cell and doubling DNA • Mitosis – dividing the nucleus and chromosomes • Stages of mitosis – TAMPA – PMAT (nonsense word) • Cytokinesis
Mitosis = separating chromatids • four main phases of mitosis: – – Prophase Metaphase Anaphase Telophase • Mitosis = separating DNA and putting a copy in each daughter cell
The mitotic spindle The structure that separates sister chromatids during mitosis Made of microtubules • hollow protein fibers • key components of cytoskeleton • attach to centromere on chromosome via kinetochore proteins
For each stage, you should know • What happens to the nuclear envelope • What happens to the chromosomes • What happen to the spindle fibers
Up close: cell cycle and mitosis Interphase
Interphase • G 1 = Growth • S = Double the DNA • G 2 = Growth
• Spindle forms Prophase • Chromatin packaged as chromosomes • Nuclear envelope breaks down
Early Prophase • Chromatin packaged into chromosomes • Two cytoskeletal structures called centrosomes begin to move toward opposite ends of the cell • mitotic spindle forms centrosomes move towards pole microtubules grow
Late Prophase • nuclear envelope breaks down • Spindle fibers attached to centromeres
Metaphase • Chromosomes line up in the middle • Why the middle? Spindle fibers pulling
Anaphase • Chromosomes are torn Apart • Spindle fibers shorten (pull chromosomes apart)
Anaphase – Chromosome pulled Apart • sister chromatids are separated Why? Microtubules get shorter • Once separated, each “chromatid” is considered a new “chromosome”
Telophase • Chromosomes are distant • “Tel” = distant Telephone Television • Nucleus reforms • Cytokinesis continues
Telophase • Chromosomes are distant • “Tel” = distant Telephone Television • Nucleus reforms • Cytokinesis continues
Telophase - New Nuclei • nuclear envelopes for each set of chromosomes • chromosomes begin to unwind (become less visible)
Mitosis: the quick review • Prophase: nucleus breaks down, chromosomes condense, spindle fibers form as centrioles move to poles • Metaphase: no nucleus, chromosomes line up at the middle as spindle fibers pull on them • anaphase: no nucleus, chromosomes torn apart by shortening spindle fibers • telophase: nucleus reforms, chromosomes begin to unwind, spindle fibers break down
starts in telophase How do cells divide? Cytokinesis “Cyto”(cell) + “kinesis”(movement) Cytokinesis • enlarged cell 2 daughter cells • each has full complement of DNA • one parent cell, into two daughter cells
Cytokinesis – different in plant & animal • animal cells - actin microfilaments contract Squeeze in middle plant cells – grow a new wall
Cancer: no checkpoints • cells divide as fast as possible • treatment – surgery – administration of chemicals: chemotherapy
Fighting cancer • Surgery to remove the cancerous tumor – not effective if cancer metastasized • Radiation therapy – high-energy radiation beams – kills dividing cells – damages DNA – triggers apoptosis
Fighting cancer • Chemotherapy – Drugs interfere with cell division • Taxol
Cancer and cell division • Taxus brevifolia, the pacific yew, is one species of a family of related evergreen trees • extract from bark kills cancer cells • Taxol
Cancer and cell division Taxol • interferes with the normal organization of microtubule • prevents microtubules from shortening • chromatids not separated
Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz Biology for a Changing World SECOND EDITION Lecture Power. Point CHAPTER 11 Single-Gene Inheritance and Meiosis
Meiosis - Why have sex? • Asexual reproduction - offspring usually identical to the parent • Same vulnerabilities • Sexual reproduction – some DNA from each parent – Similar to, but not the same as either parent – May have better combination of genes • Better chance to survive and breed
Humans are diploid have two sets of DNA (2 n) In humans n = 23 “Maternal” = from mom 1 n from mom, 1 n from dad “Paternal” = from dad Homologous = “the same as” Chromosomes in homologous pairs Chromosome 1 from dad is the same kind of chromosome as chromosome 1 from mom
Meiosis: Making cells for sex Gametes – cells for reproduction Sperm & egg haploid (1 n) 1 of each type of chromosome “one of each homologous pair of chromosomes” Meiosis = how we get Gametes “double the DNA, Divide Again”
Nerd Words for making babies Haploid (1 n) sperm + haploid (1 n) egg = diploid (2 n) zygote Made via meiosis In humans n = 23 autosomes sex chromosomes mitosis Zygote embryo adult Offspring = different from parents Gene combination neither parent has
• Gamete – sex cell, ½ the DNA of normal cell • Each cell in you ½ DNA from dad’s sperm (a gamete) ½ DNA from mom’s egg (a gamete) Cell to use in sex = made by meiosis “haploid” = one set of DNA (Half the normal amount) 1 n = only one set of DNA • “Somatic Cell” Normal cell = made by mitosis “diploid” = two sets of DNA (dad and mom) 2 n = has two sets
Meiosis: Making Gametes Special division to go from diploid to haploid 6 chromosomes Double @ S of interphase double 6 doubled chromosomes 3 doubled chromosomes divide again divide
Meiosis: Two Cell Divisions • “Double the DNA, Divide again” • Meiosis 1 – first division Separates homologous pairs • Meiosis II – second division tears chromosomes apart (like mitosis)
Meiosis spermatogenesis • Meiosis II – separates sister chromatids – four haploid daughter cells – develop into egg or sperm – Polar body vs oogenesis
Meiosis: Two Cell Divisions • Named like Mitosis • Meiosis 1 - first division Prophase I, metaphase I, anaphase I, telophase I Separates homologous pairs • Meiosis II – second division II Prophase II, metaphase II, anaphase II, telophase II tears chromosomes apart (like mitosis)
Meiosis: Terms to know • Tetrad = “group of four” Four “chromatids” = Two doubled chromosomes (these are four future chromosomes) • Metaphase Plate imaginary line in middle of cell Where chromosomes line up during metaphase
Meiosis I - separate the pairs • Each chromosome was doubled during interphase • Metaphase 1 = “Homologous pairs” line up doubled chromosomes of same kind line up together • Tetrad = another name for pairs of doubled chromosomes Four “chromatids” = four future chromosomes
Meiosis I - separate the pairs • Anaphase 1 = separate the Homologous pairs • Spindle fibers NOT in a tug of war. – Each pulls a chromosome to the pole
Meiosis II: separate doubled chromosomes • Just like mitosis • Metaphase II Line up down the Middle • Anaphase II Tear them Apart
Meiosis II: Double, Divide • Double DNA in Interphase • Meiosis I = 1 parent 2 daughter cells • Meiosis 2 = each daughter cell divides again • Total of four cells at the end exception Polar body
Compare: Mitosis & Meiosis Before Interphase Double in Interphase Divide again Mitosis 1 Parent (2 n) Temporarily 4 n End with 2 somatic cells (2 n) Meiosis 1 Parent (2 n) Temporarily 4 n Have 2 cells (2 n) End with 4 gametes, each is 1 n Meiosis & sexual reproduction creates genetic variation better chance to survive
Sex Determination • xx = female, xy = male • EACH GAMETE HAS 1!!!! • All eggs have ‘x’ • 50% of sperm have ‘y’ sex determination video
Junction/Disjunction • Junction: where things come together • Disjunction: where things separate
Non-Disjunction Things that should separate do not Often caused by broken spindle fibers
Nondisjunction: abnormal gametes
Inherited Chromosomal Abnormalities • “eu”(normal) + “ploidy”(number) = euploidy • “An” = NOT • “aneuploidy” = abnormal # of chromosomes serious abnormality for animals Often lethal for embryo Caused by problem during meiosis spindle fiber(s) can break
Aneuploidy in autosomes Big chromosomes: probably lethal to animals Small chromosomes: side effects
Aneuploidy: trisomy 21 Age of mother
Aneuploidy: trisomy 21 Father’s age matters too Advanced paternal age combined with maternal age significantly influences the incidence of Down syndrome.
Aneuploidy in sex chromosomes Effects often more minor than in autosomes • XXX • XO – Turner’s Syndrome • XXY – Kleinfelter’s syndrome • XYY • XXYY
Sexual Reproduction = Genetic Variation Three Sources Of Genetic Variation 1. Independent Assortment 2. Crossing Over 3. Random Fertilization
Gene variation: 1 independent assortment pairs line up randomly Many possible gametes (Exception: Platypus sex chromosomes are weird. Ask outside class)
Genetic Variation: 2 – crossing over ONLY MEIOSIS 1’s prophase or anaphase Paternal and maternal chromosomes can swap parts.
Crossing Over: Meiosis & Variation Increases variation Example: Four possible gametes Many chromosomes Many possible gametes Genetic recombination
Meiosis and genetic diversity • No two gametes are identical • Due to recombination and independent assortment
Genetic Variation: 3 – random fertilization Lots of sperm (more than needed for reproduction) Different gene combinations in each Most don’t get to fertilize
Summary • Cell division is, necessary for normal growth, development, and repair of the body. • The cell cycle is the sequence of steps that a cell undergoes in order to divide. Stages of the cell cycle include interphase, mitosis, and cytokinesis. • In mitosis, which takes place in several stages, replicated chromosomes segregate to opposite poles of the dividing cell; during cytokinesis, the cell physically divides into two daughter cells. • Cell cycle checkpoints ensure accurate progression through the cell cycle; repair mechanisms at each checkpoint can fix mistakes that occur, such as DNA damage. • Mistakes in the course of cell division can lead to cancer, which is unregulated cell division. • Chemotherapy drugs work by interfering with some part of the cell cycle.
Stem Cells and Germ Cells • Germ cells = cell that will be used to make gametes • Stem Cells Unspecialized (can make lots of cell types) growth, regenerate, and repair tissues
Review Questions CHAPTER 10 Cell Division
Concept Quiz Which of the following is not true about interphase? A. B. C. D. The cell grows larger during interphase. Chromosomes are duplicated during interphase. Interphase is divided into three phases. Chromosomes segregate to daughter cells during interphase.
Concept Quiz Which of the following is true about homologous chromosomes? A. Both were received from the same parent. B. One of each segregates to each daughter cell during mitosis. C. Both stay together in meiosis I. D. All 23 pairs are always homologous.
Concept Quiz Meiosis insures that A. Each gamete receives the same genes B. Chromosome number is doubled in the gametes C. Zygotes produced by fertilization have the normal number of chromosomes D. All paternal chromosomes end up in the same gamete
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