Functions of the Cell
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Basic unit of life
Protection and support
Movement
Communication
Cell metabolism and energy release
Inheritance
3-1
Cell Characteristics
• Plasma Membrane
– Outer cell boundary
– Substances inside the cell membrane
are intracellular
– Substances outside the cell are
extracellular.
– Encloses an supports the cell
contents.
3-2
Plasma Membrane
– It attaches cells to the extracellular
environment or to other cells.
– The ability of cells to recognize and
communicate with each other take
place through the plasma membrane
– It determines what moves into and
out of cells.
3-3
Plasma Membrane
• Ion movement by cells results in a charge
difference across the plasma membrane
called the MEMBRANE POTENTIAL
• The outside of the plasma membrane is
positively charged compared to the inside
because there are more positively charged
ions immediately on the outside of the
plasma membrane and more negatively
charged ions inside.
3-4
Plasma Membrane
• The membrane potential allows cells to
function like tiny batteries with a
positive and negative pole.
• It is an important feature of a living
cell’s normal function.
3-5
Plasma Membrane
• Consists of:
– 45% -50% lipids
– 45% - 50% proteins
– 4% - 8% carbohydrates
• The carbohydrates combine with
lipids to form glycolipids
• The proteins combine with lipids
to form glycoproteins.
3-6
Membrane Lipids
• 1st: Phosoplipids
• Form lipid bilayer
– Double layer of lipid molecules
– They have a polar head (exposed to
water inside and outside the cells)
and a non polar tail (face one
another in the interior of the plasma
membrane.
3-7
Membrane Lipids
• 2nd: Cholesterol
– Interspersed among the phospholipids
and accounts for about 1/3 of the total
lipids in the plasma membrane.
– The amount of cholesterol in a given
membrane is a major factor in
determining the fluid nature of the
membrane. Which is critical to its
function.
3-8
Membrane Lipids
• Phospholipids form a lipid bilayer
– Hydrophilic (water-loving) polar heads
– Hydrophobic (water-fearing) nonpolar
heads
• Cholesterol: Determines fluid nature of
membrane
3-9
Membrane Proteins
• Many functions of the plasma membrane
are determined by its proteins.
– FLUID-MOSAIC MODEL:
• The plasma membrane is neither
rigid nor static in structure.
• It is highly flexible and can change
its shape and composition through
time.
3-10
Movement through the Plasma
Membrane
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Diffusion
Osmosis
Filtration
Mediated transport mechanisms
– Facilitated diffusion
– Active transport
– Secondary active transport
3-11
Osmosis
• Diffusion of water (solvent) across a
selectively permeable membrane
• Important because large volume changes
caused by water movement disrupt normal cell
function
• Cell shrinkage or swelling
– Isotonic: cell neither shrinks nor swells
– Hypertonic: cell shrinks (crenation)
– Hypotonic: cell swells (lysis)
3-12
Filtration
• Works like a sieve
• Depends on pressure difference on
either side of partition
• Moves from side of greater pressure
to lower
–Example: In kidneys in urine
formation
3-13
Endocytosis
• Internalization of
substances by
formation of a vesicle
• Types
– Phagocytosis
– Pinocytosis
– Receptor-mediated
endocytosis
3-14
Pinocytosis
3-15
Exocytosis
• Accumulated vesicle secretions expelled from cell
• Examples
– Secretion of digestive enzymes by pancreas
– Secretion of mucus by salivary glands
– Secretion of mild by mammary glands
3-16
Cell Characteristics
• Cytoplasm
–Cytosol
–Cytoskeleton
–Cytoplasmic inclusions
3-17
Cytoplasm
• Cellular material outside
nucleus but inside plasma
membrane
• Cytosol: Fluid portion
• Cytoskeleton: Supports the
cell
– Microtubules
– Microfilaments
– Intermediate filaments
• Cytoplasmic inclusions
3-18
Organelles
• Small specialized structures for
particular functions
• Most have membranes that
separates interior of organelles
from cytoplasm
• Related to specific structure and
function of the cell
3-19
Centrioles
• In specialized zone
near nucleus:
Centrosome
• Each unit consists of
microtubules
• Before cell division,
centrioles divide,
move to ends of cell
and become spindle
fibers
3-20
Cilia
• Appendages projecting
from cell surfaces
• Capable of movement
• Moves materials over
the cell surface
3-21
Flagella
• Similar to cilia
but longer
• Usually only one
exists per cell
• Move the cell
itself in wavelike
fashion
• Example: Sperm
cell
3-22
Microvilli
• Extension of plasma
membrane
• Increase the cell
surface
• Normally many on
each cell
• One tenth to one
twentieth size of
cilia
• Do not move
3-23
Ribosomes
• Sites of protein
synthesis
• Composed of a large
and small subunit
• Types
– Free
– Attached to
endoplasmic
reticulum
3-24
Endoplasmic
Reticulum
• Types
– Rough
• Attached ribosomes
• Proteins produced
and modified
– Smooth
• Not attached
ribosomes
• Manufacture lipids
• Cisternae: Interior spaces
isolated from rest of
cytoplasm
3-25
Golgi Apparatus
• Modification,
packaging,
distribution of
proteins and
lipids for
secretion or
internal use
• Flattened
membrane sacs
stacked on each
other
3-26
Mitochondria
• Provide energy for
cell
• Major site of ATP
synthesis
• Membranes
– Cristae:
Infoldings of
inner membrane
– Matrix:
Substance
located in space
formed by inner
3-27
membrane
Nucleus
• DNA dispersed throughout
• Consists of :
– Nuclear envelope: Separates nucleus from cytoplasm
and regulates movement of materials in and out
– Chromatin: Condenses to form chromosomes during
cell division
– Nucleolus: Assembly site of large and small
ribosomal units
3-28
Chromosome Structure
3-29
Overview of Cell Metabolism
3-30
Overview of Protein Synthesis
3-31
Overview of Protein
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Synthesis
Transcription
– Copies DNA to
form mRNA
– tRNA carries
amino acids to
ribosome
• Translation
– Synthesis of a
protein at
ribosome
3-32
Translation
3-33
Cell Life Cycle
• Interphase
– Phase between
cell divisions
• Mitosis
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis
– Division of cell
cytoplasm 3-34
Mitosis
3-35
Mitosis
3-36
Meiosis
3-37
Cellular Aspects of Aging
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Cellular clock
Death genes
DNA damage
Free radicals
Mitochondrial damage
3-38