Eukaryotic Cells

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Chapter 1
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Eukaryotic Cells

• Have a nucleus and other organelles
• Eukaryotic organisms
• Plants
• Animals (humans)
• Protistans
• Fungi

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Functions of Nucleus

• Keeps the DNA separated from metabolic machinery
  of cytoplasm
• Makes it easier to organize DNA and to copy it
  before parent cells divide into daughter cells

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Components of Nucleus
Nuclear envelope Nucleoplasm Nucleolus Chromatin
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Chromatin

• Cells collection of DNA and associated proteins
• Chromosome is one DNA molecule and its associated
  proteins (chromatids are a pair)
• Appearance changes as cell divides

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Nuclear Envelope

• Two outer membranes (lipid bilayers)
• Innermost surface has DNA attachment sites
• Pores span bilayer

one of two lipid bilayers (facing nucleoplasm)
NUCLEAR ENVELOPE
one of two lipid bilayers (facing nucleoplasm)
nuclear pore (protein complex that spans both
lipid bilayers)
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Nucleolus

• Dense mass of material in nucleus
• May be one or more
• Cluster of DNA and proteins
• Materials from which ribosomal subunits are built
• Subunits must pass through nuclear pores to reach
  cytoplasm

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Endomembrane System

• Group of related organelles in which lipids are
  assembled and new polypeptide chains are modified
  (proteins)
• Products are sorted and shipped to various
  destinations (FedEx??)

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Components of Endomembrane System

• Endoplasmic reticulum
• Golgi bodies
• Vesicles

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Endoplasmic Reticulum

• Continuous with nuclear membrane
• Extends throughout cytoplasm
• Two regions rough and smooth

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Rough ER

• Arranged into flattened sacs
• Ribosomes on surface give it a rough appearance
• Some polypeptide chains enter rough ER and are
  modified
• Cells that specialize in secreting proteins have
  lots of rough ER

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Smooth ER

• A series of interconnected tubules
• No surface ribosomes
• Lipids assembled inside
• Smooth ER of liver needed
• in detox.

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Golgi Bodies

• Put finishing touches on proteins and lipids that
  arrive from ER
• Package finished material for shipment to final
  destinations
• Material arrives and leaves in vesicles

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Vesicles

• Membranous sacs that move through the cytoplasm
• Lysosomes
• Peroxisomes

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Central Vacuole

• Fluid-filled organelle
• Stores amino acids, sugars, wastes
• As cell grows, expansion of vacuole as a result
  of fluid pressure forces cell wall to expand
• In mature cell, central vacuole takes up 50-90
  percent of cell interior

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Mitochondria

• ATP-producing powerhouses
• Double-membrane system
• Carry out the most efficient energy-releasing
  reactions
• These reactions require oxygen

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Mitochondrial Structure

• Outer membrane faces cytoplasm
• Inner membrane folds back on itself
• Membranes form two compartments
• ATP-making machinery is embedded in the inner
  mitochondrial membrane

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Cell Cycle
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Reproduction

• Parents produce a new generation of cells or
  multicelled individuals like themselves
• Parents must provide daughter cells with
  hereditary instructions, encoded in DNA, and
  enough metabolic machinery to start up their own
  operation

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Division Mechanisms

• Eukaryotic organisms
• Mitosis
• Meiosis
• Prokaryotic organisms
• Prokaryotic fission

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Roles of Mitosis

• Multicelled organisms
• Growth
• Cell replacement
• Some protistans, fungi, plants, animals
• Asexual reproduction

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Meiosis

• Functions only in sexual reproduction
• Precedes the formation of gametes (sperm and
  eggs) or spores

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Chromosome

• A DNA molecule attached proteins
• Duplicated in preparation for mitosis

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Sister Chromatids

• Each chromosome and its copy stay attached to
  each other as sister chromatids until late in the
  nuclear division process
• Attach at the centromere

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Nucleosome

• A nucleosome consists of part of a DNA molecule
  looped twice around a core of histone proteins

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Organization of Chromosomes
DNA
one nucleosome
DNA and proteins arranged as cylindrical fiber
histone
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Cell Cycle

• Cycle starts when a new cell forms
• During cycle, cell increases in mass and
  duplicates its chromosomes
• Cycle ends when the new cell divides

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Interphase

• Usually longest part of the cycle
• Cell increases in mass
• Number of cytoplasmic components doubles
• DNA is duplicated

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Stages of Interphase
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Control of the Cycle

• Once S begins, the cycle automatically runs
  through G2 and mitosis
• The cycle has a built-in molecular brake in G1
• Cancer involves a loss of control over the
  cycle, malfunction of the brakes

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Stopping the Cycle

• Some cells normally stop in interphase
• Neurons in human brain
• Arrested cells do not divide
• Adverse conditions can stop cycle
• Nutrient-deprived amoebas get stuck in interphase

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Chromosome Number

• Sum total of chromosomes in a cell
• Somatic cells
• Chromosome number is diploid (2n)
• Two of each type of chromosome
• Gametes
• Chromosome number is haploid (n)
• One of each chromosome type

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Human Chromosome Number

• Diploid chromosome number (n) 46
• Two sets of 23 chromosomes each
• One set from father
• One set from mother
• Mitosis produces cells with 46 chromosomes two
  of each type

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Lots of DNA

• Stretched out, the DNA from one human somatic
  cell would be more than two meters long
• A single line of DNA from a salamander cell would
  extend for ten meters

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Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Bipolar Mitotic Spindle

• Consists of two distinct sets of microtubules
• Each set extends from one of the cell poles
• Two sets overlap at spindle equator
• Moves chromosomes during mitosis

microtubule of bipolar spindle
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Mitosis

• Period of nuclear division
• Usually followed by cytoplasmic division
• Four stages
• Prophase
• Metaphase
• Anaphase
• Telophase

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Early Prophase - Mitosis Begins

• Duplicated chromosomes begin to condense

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Late Prophase

• New microtubules are assembled
• One centriole pair is moved toward opposite pole
  of spindle
• Nuclear envelope starts to break up

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Transition to Metaphase

• Spindle forms
• Spindle microtubules become attached to the two
  sister chromatids of each chromosome

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Metaphase

• All chromosomes are lined up at the spindle
  equator
• Chromosomes are maximally condensed

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Anaphase

• Sister chromatids of each chromosome are pulled
  apart
• Once separated, each chromatid is a chromosome

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Telophase

• Chromosomes decondense
• Two nuclear membranes form, one around each set
  of unduplicated chromosomes

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Results of Mitosis

• Two daughter nuclei
• Each with same chromosome number as parent cell
• Chromosomes in unduplicated form

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Cytoplasmic Division

• Usually occurs between late anaphase and end of
  telophase
• Two mechanisms
• Cleavage (animals)
• Cell plate formation (plants)

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Animal Cell Division
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Fig. 01-05
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Fig. 01-07
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Fig. 01-08
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Fig. 01-09
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Fig. 01-11
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Fig. 1A
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Fig. 01-16
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Fig. 1B