Transcript The Amazing Cell

The Amazing Cell
Chapter 3
Anatomy and Physiology
Cells
• Basic unit of living things.
• Can exist alone as a single, free, living plant or
animal, or can combine to form elaborate and
complex organisms.
• Multicellular organisms are when cells have
differentiated and become grouped into specialized
tissues that work collaboratively to sustain life for
the animal as a whole.
• We must understand the cell before we can
understand the anatomy and physiology of the
tissues and systems the cell makes up
Evolution of Cells
• Evolved about 3 billion years ago.
• Primitive cells are thought to have resembled
present-day bacteria and contained a single strand
of DNA in a gelatinous protoplasm.
• Prokaryotes- “before nucleus”, cells without
nucleus were thought to have developed first.
• Has DNA but not in a separate compartment
• Eukaryotes- “true nucleus”, developed later and are
found in all multicellular organisms.
• Has distinct nucleus surrounded by protective
nuclear envelope.
Size Limitations
• Size of most cells is restricted to 10-30 µm in
diameter because of relationship between surface
area and volume of a cell.
• Why is this important:
• Smaller cells can feed themselves efficiently to
carry on functions.
• Large cells could not take in nutrients fast
enough to support cell and would therefore die.
• Also a small cell is better governed by a single
nucleus. Larger cells need multiple nuclei.
• What is an example of this and why?
Mammalian Cell Anatomy
• Contain essential structures:
• Cell membrane (also known as plasma
membrane).
• Separates cell from environment.
• Cytoplasm
• Everything inside the cell membrane
aside from nucleus and genetic
material.
• Nucleus
• Contains the genetic material of the
cell.
Other optional parts of a cell
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Cilia
Mitochondria
Endoplasmic Reticulum (ER)
Ribosomes
Golgi apparatus
Lysosome
Peroxisomes
Cell Membrane
• Flexible, elastic barrier between inner
cytoplasm and outer environment.
• Contains infoldings and outpouchings that
provide extra surface area.
• Why is this important?
• Capable of self-repair.
• Governs the movement of atoms and
molecules in and out of the cell.
• Consists primarily of protein,
phospholipids, cholesterol,lipids, and
carbohydrates.
Membrane Structure
• Lipid bilayer: composed of two layers of phospholipid molecules
• Hydrophilic “heads” are on outside
• Hydrophobic fatty acid “tails” are on
the inside
• Most lipid soluble molecules easily
pass through membrane
• Water-soluble molecules do not
readily pass through
• Fluid mosaic: Proteins suspended in bilayer and move easily throughout
membrane to create a constantly changing pattern
Cell Membrane Structure
Continued
• Composed of Structural and Globular
proteins.
• What are these also called?
• What do they do?
• Proteins that occur within the bilayer are
called integral proteins.
• Globular proteins that span the entire
width of the membrane and may create
channels through which other
molecules can pass.
Integral Proteins
• Channels they create may be:
• Selective
• permit only certain molecules in or out of the
cell
• Pores
• allow the passage of molecules freely
Peripheral Proteins
• Type of globular protein which can be
bound to the inside or outside surfaces of
the cell membrane.
• Sometimes act as enzymes
• May be involved in changing the cell’s
shape (muscle contraction).
Cell Membrane: External Surface
• Glycocalyx – coating on the cell surface of some
cells made of glycoprotein and glycolipids.
• Unique to each cell – provides markers for
recognition and for interactions.
• Composed of 2 groups of molecules:
• Cell Adhesion Molecules (CAMs)
• Sticky glycoproteins that cover cell
surface. Help cells move past one
another and signaling.
• Signal circulating cells like WBCs to
areas of inflammation or infection
• Membrane Receptors
• Integral proteins and glycoproteins that
act as binding sites on the cell surface.
• Involved with signaling as well.
Flagella and Cilia
• Extensions of the plasma membrane that extend
into the extracellular space.
• Both contain 9 pairs of microtubules that encircle a
central pair of microtubules.
• Cilia- occur in large numbers on the exposed
surface of some cells. Shorter than flagella and
move synchronously to create waves of motion for
propulsion.
• Functions:
• In upper respiratory tract, propel bacteria
and mucus from the lungs
• In oviduct, pulls egg from ovary into oviduct.
• Flagella- significantly longer than cilia and
usually occur singularly.
• Attached to individual cells and aid in
propulsion.
• Example:
• Tail of sperm is flagellum
Cytoplasm
• The inner substance of the cell, excluding
the nucleus.
• Components include:
• Cytosol
• Cytoskeleton
• Organelles
• Inclusions
Cytosol
• The fluid of the cell
• Viscous, semi-transparent liquid
composed of dissolved electrolytes, amino
acids, and simple sugars.
• Proteins suspended within fluid give fluid
its thick, jellylike consistency.
• Are enzymes that are important in
metabolic activities of the cell.
Cytoskeleton
• Three dimensional frame for the cells, is neither
rigid or permanent.
• Flexible and fibrous and changes in accordance to
activities of the cell.
• Gives support and shape to the cell, enables cell to
move and provides direction for metabolic activity.
• Also anchors organelles.
• Types of fibers that comprise cytoskeleton:
• Microtubules
• Intermediate fibers
• Microfilaments.
• Microtubules
• Thickest fibers and are long and hollow
• Form cables that organelles attach too.
• Proteins move these organelles along
microtubules throughout cell.
• Can be easily disassembled and
reasembled to form new paths or take
on new direction.
• Composed of tubulins.
• Intermediate fibers
• Woven, ropelike fibers that possess
high tensile strength and are able to
resist pulling forces on the cell by acting
as internal guy wires.
• Toughest and most permament part of
the cytoskeleton.
• Composed of proteins
• May take on different names:
• Tonofilaments-in epithelial cells
• Neurofilaments- in nerve cells
• Microfilaments
• Located near cell surface on the cytoplasmic
side of the plasma membrane and are arranged
in bundles and meshworks.
• Composed of actin and myosin
• Play key role in cell’s ability to change shape,
break apart during cell division and form
outpouchings and involutions.
• Are assembled where and when needed.
• Depends on what cell is doing as to how many
are found within cell.
Organelles
• “little organs”
• Membrane bound structures within
cytoplasm that have specialized functions.
• Is separated from cytoplasm by own
membrane so can maintain own internal
environment.
• Compartmentalization is good for
metabolic processes such as food
absorption, energy production, and
excretion.
Organelles continued
• Include:
• Mitochondria
• Ribosomes
• Golgi Apparatus
• Endoplasmic Reticulum
• Lysosomes
• Peroxisomes
Mitochondria
• One of largest organelles
• Called “powerhouse of the cell” because
produces up to 95% of energy that fuels
the cell.
• Nutrient molecules (i.e. glucose) are
broken down to produce intracellular fuel.
• Location of many biochemical reactions.
• Amino acid and fat catabolism
• Where respiration takes place
• What is this?
Mitochondria continued.
• Active cells have higher energy demands
so have more mitochondria.
• Heart cells
• Mitochondria can divide through fission-or
the pinching itself in half.
• Tend to be located at portion of cell
where energy requirements are the
greatest.
• Contain DNA, RNA and enzymes.
• Provide selves with 13 proteins while
nucleus provides the remainder.
Mitochondrial shape
• Tend to be elliptical and round with
outer smooth membrane and inner
involuted membrane.
• Inner membrane forms cristae which
increase internal working area and
matrix (enzyme-rich liquid housed in
mitochondria).
• Cristae are site of ATP production
• what does this do?
Ribosomes
• Most common organelle in the cell.
• Made of two globular subunits composed
of protein and rRNA.
• Important in protein synthesis.
• Can attach and detach from membranes
and move freely within the cell.
• Move back and forth depending on type
of protein they are making between
endoplasmic reticulum and
cytoskeleton.
Endoplasmic Reticulum (ER)
• Series of flattened tubes stacked on one another
and bent into crescent shape.
• Composed of single lipid bilayer
• May be rough or smooth depending on if it contains
ribosomes or not.
• Rough ER is involved in production of protein.
• Smooth ER is connected to Rough ER and is
active in synthesis and storage of lipids.
• In liver may also break down drugs and
break down glycogen into glucose.
Golgi Apparatus
• Found near nucleus and is similar in
structure to ER (composed of cisternae)
• Receives proteins produced by ER.
• Proteins are modified here as they move
from fold to fold.
• Once completed they are packages in
vesicles and travel out into cell or to cell
membrane.
Lysosomes
• Specialized vesicle formed by Golgi apparatus.
• Contains hydrolytic enzymes which engulf bacteria
or cell nutrients and digests them.
• Principal responsibility to breakdown nutrient
molecules.
• Considered “stomach of the cell”.
• When cells die, lysosomes are released and digest
other portions of the cell, this is called autolysis.
• May also release enzymes outside of cell to assist
with breakdown of extracellular material.
Peroxisomes
• Membranous sacs containing enzymes found
throughout the cell.
• Reproduce through fission.
• Important in detoxification of various molecules.
• Remove free radicals- normal products of
cellular metabolism but can be harmful in large
numbers
• Carry two major enzymes:
• Peroxidases-assist in conversion in free
radicals to hydrogen peroxide.
• Catalases-reduce hydrogen peroxide to water.
Inclusions
• Packaged units of metabolic products or
substances that the cell has engulfed.
• May or may not be membrane-bound.
• Vacuoles are larger than vesicles but are
of similar structure.
Centrioles
• Small, hollow-like cylinders composed of
microtubules.
• Found in pairs perpendicular to one
another.
• Visible during cell division near nuclear
envelope
• Help to organize spindle fibers during cell
division.
• May also form bases of cilia and flagella
(basal bodies).
Nucleus
• Largest organelle in the cell.
• Control center or “brain” of the cell.
• Primary functions are to maintain
hereditary information of the species and
to control cellular activities through protein
synthesis.
• Some cells may be multi-nucleated while
some are anucleated.
• What is this and where is it found?
• What is a disadvantage to no nucleus?
Nuclear Anatomy
• Divided into four parts:
• Nuclear Envelope or membrane
• Nucleoplasm
• Chromatin
• Nucleoli
Nuclear Envelope and
Nucleoplasm
• Separated from cytosol by a
nuclear envelope composed of
two lipid bilayers
• Outer layer is continuous with
Rough ER.
• Contains nuclear poreschannel through entire
thickness.
• Allow transport of protein
and RNA.
• Area between bilayers is space
called perinuclear space.
Nucleoplasm
• The gel-like substance that fills the
nucleus.
• Resembles cytosol.
DNA, RNA and Chromatin
• DNA and RNA are composed of
nucleotides.
• What are they?
• How do they pair?
• What does DNA form?
• Chromatin-fibers made up of DNA and
globular proteins called histones
• Nucleosome- single strand of DNA wound
around 8 histone molecules.
• During cell divison, chromatin condenses
into super-coiled, x-shaped structure
called chromosomes.
Nucleoli
• Not membrane bound
• Where ribosomal subunits are made
• Contain DNA that governs synthesis of
rRNA.
Cell Physiology
• The Cellular Environment
• Body Fluids
• Composed primarily of water
• Intracellular fluid- fluid found inside
cell.
• Extracellular fluid- fluid outside cell.
• Interstitial fluid- fluid contained within
the tissue, except for blood found
within lymph and blood vessels.
Ions, Electrolytes, and pH
• What are ions?
• Cations
• Anions
• Electrolytes
• In sick or injured animals, electrolyte
concentrations and pH of intracellular and
extracellular fluid can become abnormally
high or low
Membrane Processes: Excretion
and Absorption
• In order to maintain homeostasis cell must
select what it needs from extracellular fluid
and bring it into intracellular environment.
• Must excrete waste products or transport
resources needed in other parts of the
body to the extracellular compartment.
• Processes may be passive (do not require
ATP) or active (do use ATP).
Passive Transport Processes
• Remember: No Energy Required!
• 4 Passive Processes:
• Diffusion
• Facilitated Diffusion
• Osmosis
• Filtration
Diffusion
• Kinetic movement of molecules from higher to
lower concentration via concentration gradient- the
difference between the concentration of one area
and the concentration of another.
• Will continue until the molecule is evenly dispersed
throughout the solution
• Determining factors for Diffusion thru a membrane:
1. Molecular size – small can move through
2. Lipid solubility – lipids can pass lipid bilayer
3. Molecular charge – ions move through special
channel proteins
4. Temperature – faster in hot solution
Facilitated Diffusion
• Selective carrier proteins assist in
movement of molecules from higher to
lower concentration; speed of diffusion is
limited by saturation of carrier molecules.
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Osmosis
• Passive movement of water through a
semipermeable membrane from dilute
solution to more concentrated one.
• Opposite of diffusion as water, not solute
is moving. Also requires semipermeable
membrane.
Filtration
• Hydrostatic pressure (caused by the
beating heart) forces liquid and small
molecules through a membrane.
• Liquids pushed through a membrane when
the pressure on one side is greater than
that on the other side.
• Example?
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Tonicity Terminology
• Isotonic : Extracellular fluid has same
concentration of dissolved substances as
intracellular fluid
• Hypotonic: Cytoplasm (inside) of cell is
more concentrated than extracellular
(outside) fluid
• Hypertonic: Extracellular fluid is more
concentrated than cytoplasm
Active Transport Processes
• Remember: Requires Energy (ATP)!
• Relies on a carrier protein with a specific binding
site
• Does not require a concentration gradient
• Symport system – substances are moving in the
same direction
• Antiport system – substances are moved in
opposite directions
• Include:
• Active Transport
• Endocytosis
• Phagocytosis
• Pinocytosis
• Receptor mediated
• Exocytosis
Active Transport
• Active movement of molecules by specific
carrier protein; molecules may move
against concentration gradient.
Endocytosis
• Phagocytosis
• Cells engulf solid substances
• Pinocytosis
• Cells engulf liquid substances
• Receptor mediated
• Specialized protein receptors bind to
ligands specific receptors.
• Ligand-small molecules that bond to
larger chemical groups or molecules.
Exocytosis
• Excretion of waste products and secretion
of manufactured substances.
• Packaged in secretory vesicles which fuse
with cell membrane and are ejected to
extracellular space.
Life Cycle of the Cell
• Two types of division of cells.
• Meiosis- Reduction division
• Found in reproductive cells. End up
with half of what start with.
• Mitosis- exact replication of cell.
• We will focus mainly on Mitosis for this
chapter.
Mitosis
• Life cycle has been divided into two major periods:
• Interphase
• When cell is growing, maturing, and
differentiating.
• Cells spend majority of time in this phase.
• Mitotic Phase
• When cell is actively dividing.
• Composed of:
• Prophase
• Metaphase
• Anaphase
• Telophase
Interphase
• Period between cell divisions.
• Nucleus and nucleoli are visible and
chromatin is arranged loosely throughout
the nucleus.
• Divided into three subphases:
• Growth 1 (G1)- metabolic activity and
cell growth; time variable (min-yrs)
depending on cell type
• Synthetic (S)- DNA replication
• Growth 2 (G2)- very brief; synthesis of
enzymes and proteins needed for
mitosis
DNA Replication
• Many cells are continually replicating to maintain body tissues,
to heal wounds, or to enable growth
• DNA must be replicated before the cell can divide – a copy of
DNA is made to be passed to the daughter cell
• Occurs during Interphase
DNA Replication
•
Process:
• Enzymes called DNA helicases pull apart the parental DNA
double helix so the bases no longer form base pairs
• Next, enzymes called DNA polymerases move along each
separated parental DNA strand and match each base on the
strand with free nucleotides that have a complimentary base (an
A is matched with a T)
• Then, DNA polymerase connects the free nucleotides together to
form new DNA strands
• When replication is complete, the parental strand and the new
strand wind together to form a double helix
• The lead strand, is made continuously; the second (lagging)
strand is made in segments, and
• DNA ligase joins the segments
• The identical DNA strands become chromatids, joined together
at the centromere to form a chromosome
Lead and Lagging Strands
Mitotic Phase- Cell Division
• Cytokinesis- division of the
cytoplasm.
• Prophase
• Chromatin coils and are
composed of two identical
chromatids
• Spindle apparatus appears
• Normal synthetic processes
cease.
• Nuclear envelope disintegrates
• Metaphase
• Chromosomes are lined up
in center of spindle.
• Centromere of each
chromosome is attached to
a spindle fiber.
• Anaphase
• Centromeres split apart and each
chromatid becomes its own
chromosome.
• Spindle fiber separates, and
chromosomes are pulled away from
each other.
• Cytoplasm constricts along metaphase
plate.
• Telophase
• Final stage of mitosis
• When chromosomal movement stops
• Chromosomes reach poles and begin
to unravel.
• New nuclear envelope appears as well
nucleoli.
• Cytokinesis ends telophase.
• New daughter cells enter interphase.
Control of Cell Division
• Some cells divide rapidly others not so
fast.
• Examples of each
• Normal cells stop dividing when they come
into contact with surrounding cells.
• Called Contact inhibition
• Division can be controlled once numbers
reach a certain point.
• Proteins can also allow cells to enter
mitotic phase
Protein Synthesis
• Protein synthesis is essential for life.
• Begins in nucleus
• tRNA transcribes DNA information
• Transcription-Genetic information in DNA is
copied onto messenger RNA (mRNA)
• Codon- series of 3 RNA nucleotides.
• mRNA sends information to cytoplasm
• Translation- Ribosomes bind to mRNA
strand (rRNA).
• New protein building as codes are
translated from nucleotides to amino acids
Genetic Mutations
• A genetic error.
• Mutations may be so severe that cell dies, but may
also cause no issues whatsoever.
• Some can be repaired by repair enzymes.
• May occur spontaneously or due to mutagens.
• Viruses
• Ionizing radiation
• Certain chemicals
• What is cancer?
• What is chemotherapy?
Cell Differentiation and
Development
• Differentiation- The progressive acquisition
of individual characteristics by cells to
enable them to perform different functions.
• Differentiation is important as it keeps cells
focused on a particular function.
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