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Introducing Cells

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Title: Introducing Cells


1
Introducing Cells
  • Cell Theory
  • Microscopy
  • Cell organelles
  • Cell organelle function

2
The Cell
  • To understand life in a useful and meaningful
    way, you have to understand the cell.

3
Seeing the big picture
  • Chemistry (atoms and molecules)
  • Cells
  • Tissue
  • Organ
  • Organism
  • Biosphere

4
The Cell Theory
  • Although different living things may be as unlike
    as a violet and an octopus, they are all built in
    essentially the same way.
  • The most basic similarity is that all living
    things are composed of one or more cells. This
    is known as the Cell Theory.
  • Prokayrotic bacteria
  • Eukaryotic (true nucleus)
  • animal
  • plant
  • fungus
  • Cells are the building
  • blocks of life.

5
The Cell Theory
  • The Cell Theory can be summarized as
  • A. All living organisms are made up of one or
    more cells
  • B. The cell is the basic unit of life
  • All cells come from the division of pre-existing
    cells
  • our knowledge of cells is built on work done with
    microscopes
  • cells come in many shapes and sizes, although
    most are microscopic
  • most cells are small, about 0.001 cm in length
    (1/100 of a mm, or 10 ?m).

6
  • Some cells are large. e.g. some giant algal
    cells may be several centimeters long. A
    chicken's egg is a single cell.
  • 40,000 red blood cells would fill the letter "O"
    on a page of type. You produce about 2.5 million
    new red blood cells every second! Each square cm
    of your skin contains about 150,000 skin cells.
  • Human beings are composed of about 50 to 100
    trillion cells.
  • cells carry on all the processes associated with
    life, such as reproducing and interacting with
    the environment.

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8
microscopes
  • Sizes of cells, viruses, and other small things
    Biology is a visually rich subject area. However,
    many of the most interesting biological events
    and structures are smaller than the unaided human
    eye can see.
  • In fact, human eyes have a resolution of about
    100 µm. On the chart below, notice that of all
    the structures listed, only the plant cell is
    within our resolution--just barely

9
EUCARYOTIC CELL STRUCTURE
  • At the most basic level, the cell's overall
    structure can be viewed as
  • 1. Cell Membrane
  • 2. Nucleus
  • 3. Organelles
  • 4. Cytoplasm
  • 1. Cell Membrane the thin layer which separates
    the cell contents from it's environment.
  • 2. Nucleus specialized structure within the
    cell which contains DNA and controls cell
    functioning and reproduction.
  • 3. Organelles small bodies with specific
    structures and functions within the cell.
  • 4. Cytoplasm the liquid substance between the
    nucleus and the cell membrane, in which the
    organelles are located.

10
Eukaryotic Cells
  • liver cell

11
Now Lets Have a DETAILED look at CELL
ORGANELLESThe Cell Membrane and the Fluid
Mosaic Model
  • the cell membrane functions in transport of
    materials in and out of cell, recognition,
    communication, and homeostasis.
  • The Fluid Mosaic
  • Model
  • Cells are surrounded
  • by a thin membrane of
  • lipid and protein.

12
  • scientists today agree upon The Fluid Mosaic
    Model of membrane structure. The cell membrane
    is a remarkable structure that has properties of
    a solid and a liquid.
  • It forms a "fluid sea" in which proteins and
    other molecules like other lipids or
    carbohydrates are suspended (like icebergs) or
    anchored at various points on its surface.
  • the sea or fluid parts composed of side by
    side phospholipids arranged in a bilayer (called
    a lipid bilayer).
  • The solid part (the mosaic)
  • is the variety of proteins etc.
  • embedded in the bilayer.

13
Cell Membrane
  • each phospholipid has a
  • hydrophobic tail and a
  • 2. hydrophylic head.
  • the membrane has consistency of
  • light machine oil.
  • the membrane is SELECTIVELY PERMEABLE (will let
    some substances in but not others of the same
    size).

14
Nucleus
15
Nucleus
  • The nucleus is a large, centrally located
    organelle surrounded by nuclear envelope.
  • The nuclear envelope is a double membrane (2
    phospholipid bilayers) that has pores.
  • Nuclear pores allow proteins into the nucleus and
    ribosomal subunits out.
  • The envelope is very porous and is a continuation
    of the membranes of the endoplasmic reticulum.

16
Nucleus
  • Double-membrane (envelope)
  • Numerous pores
  • RNA and other chemicals to pass to cytoplasm, but
    not
  • DNA

Structure of the nuclear envelope and nuclear
pores.
17
The Nucleus
  • control center or "brain" of cell. The site
    where genetic information is stored in
    chromosomes.
  • Although each cell gets a copy of every gene,
    only certain ones are turned on in a particular
    cell.
  • The DNA is contained by a number of chromosomes,
    which consist of long strands of DNA tightly
    wound into coils with proteins called histones.
    The combination of DNA and histone proteins is
    known as CHROMATIN.

18
The Nucleus
  • Genes contain DNA which works with RNA to bring
    about the synthesis of proteins
  • The nucleus, therefore, determines the
    metabolism, growth, differentiation, structure,
    and reproduction of cell.
  • The nucleolus( 1-2 darker bodies), is the site of
    rRNA synthesis (protein to from ribosomes).

19
Ribosomes
  • Site for PROTEIN SYNTHESIS !!
  • Ribosomes consist of rRNA
  • and proteins
  • each ribosome is made of 2 non-identical subunits
    (small and large)
  • rRNA is produced in the nucleolus and joined with
    proteins -- then migrate through the nuclear pore
    to the cytoplasm for final assembly
  • ribosomes attach themselves to the endoplasmic
    reticulum

20
Endoplasmic Reticulum (ER)
  • the ER is a system of MEMBRANOUS TUBULAR CANALS
    that begins just outside the nucleus and branches
    throughout the cytoplasm.
  • Part of the ER is studded with ribosomes and
    called
  • ROUGH Endoplasmic Reticulum
  • The areas without ribosomes is called SMOOTH
    Endoplasmic Reticulum.

21
Endoplasmic Reticulum (ER)
  • Both rough and smooth ER are involved in
    synthesis and modification of macromolecules.
  • Rough ER is the site where PROTEIN SYNTHESIS
    occurs on the attached ribosomes.
  • Smooth ER produces different molecules depending
    on the type of cell.

22
Smooth Endoplasmic Reticulum
  • Function 1 Synthesis of lipids
  • Ex. Smooth ER is abundant in testes and adrenal
    cortex , both of which produce steroid hormones
    (e.g. testosterone)
  • Sometimes referred to as the cells membrane
    factory b/c it is where phospholipids are
    synthesized.
  • Function 2 Detoxification of Drugs
  • Ex. In liver cells the smooth ER is capable of
    releasing enzymes that can detoxify substance
    such as alcohol.
  • It does this through attached peroxisomes that
    contain detoxification enzymes).

23
Endoplasmic Reticulum (ER)
  • Most of the macromolecules (proteins, lipids,
    etc) leaving the endoplasmic reticulum are still
    not mature.
  • They must undergo further processing in another
    organelle, the Golgi apparatus, before they are
    ready to perform their functions within or
    outside the cell. (fig. 3.6 p. 55)

24
Golgi Apparatus
  • The Golgi Apparatus (X in diagram),
  • are stacks of flattened, hollow cavities
  • enclosed by membranes, which are
  • often continuous with the membranes
  • of the endoplasmic reticulum.
  • located near to the nucleus and ER.
  • Looks like a flattened stack of hollow tubes.

25
Golgi Apparatus
  • Thus, the Golgi apparatus functions in protein
  • 1. Modification (i.e. addition of a
    carbohydrate or phosphate group)
  • 2. Packaging (often in secretory vesicles
    that move to plasma membrane)
  • 3. Secretion (of substances to cytoplasm or
    export from the cell)
  • it receives newly manufactured protein (from the
    ER) on it's inner surface.
  • Within the Golgi apparatus, the proteins are
    sorted out, labeled, and packaged into vesicles
    that "pinch off" the outer surface into vesicles.
  • These vesicles can then be transported to where
    they are needed within the cell, or can move to
    the cell membrane for export to the outside of
    the cell by exocytosis (i.e hormone secretion)
  • See figure 3.6 in text

26
Vacuoles and Vesicles Storage Transport
  • a VACUOLE is a large membrane-enclosed sac
  • a VESICLE is a small membrane-enclosed sac
  • vacuoles and vesicles are formed by
  • 1) pinching off from the Golgi apparatus or ER
  • 2) Endocytosis (pinching in of cell membrane to
    import)
  • are used for transport and storage of materials
  • lysosomes are examples of a vesicle
  • peroxisomes are an example of a vacuole

27
Lysosomes
  • Lysosomes Cellular Stomachs
  • specialized vesicles which are formed by the
    Golgi apparatus.
  • contain powerful hydrolytic enzymes functions in
  • cellular digestion
  • autodigestion or disposal of damaged cell
    components like mitochondria. (e.g. in
    development of embryo-fingers)
  • breakdown of a whole cell (by releasing their
    contents into the cell cytoplasm). For this
    reason, they are sometimes called suicide sacs.

28
Lysosomes
  • Lysosomes are known to contain over 40 different
    enzymes that can digest almost anything in the
    cell, including proteins, RNA, DNA, and
    carbohydrates.
  • Lysosomes help destroy invading bacteria.

29
Peroxisomes
  • PEROXISOMES are also single-membrane organelles
    (Vacuoles).
  • contain enzymes which are able to react with
    toxic substances and break them down. Detoxify
  • i.e. alcohol in liver cells

30
Mitochondria
  • The Cells Powerhouse
  • generates energy (ATP) for the cell by burning
    sugar (glucose).
  • Mitochondria are the largest organelles in an
    animal cell, after the nucleus (about the size of
    bacteria).
  • Are sausage-shaped or filamentous structures
    surrounded by a double-layered membrane.

31
Mitochondria
  • The mitochondrion has two membranes an outer
    and an inner.
  • The inner is convoluted into shelf-like folds
    called cristae.
  • The enzymes responsible for cellular
    respiration are arranged, in assembly-line
    fashion, on the cristae.

32
Mitochondria
cristae
matrix
  • Function AEROBIC ENERGY METABOLISM (AKA
    CELLULAR RESPIRATION). Converts glucose and
    fatty acids to ATP ENERGY!
  • The overall formula for cellular respiration is
  • Carbohydrate O2 CO2 H2O
    ENERGY
  • In the end, 38 molecules of ATP (adenosine
    triphosphate) are formed for every molecule of
    glucose that is used up in respiration.

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