Download Cell Structure and Function Chapter 4 Biology 100

CELL STRUCTURE AND FUNCTION
CHAPTER 4
BIOLOGY 100
DISCOVERY OF THE CELL
Robert Hooke used a
simple kind of
microscope to study
slices of cork in 1664.
 He saw many cubicles
fitting neatly together



Hooke called these cells.
van Leeuwenhoek was
the first to see living
cells and later was first
to see bacteria
Van Leeuwenhoek’s microscope
THE CELL THEORY

Schleiden and Schwann came up with the theory
in the 1830’s


All living things are made of cells
Virchow added in 1855 to the cell theory

New cells are formed only from division of preexisting cells, not spontaneous generation
DIFFERENCES AND SIMILARITIES OF
CELLS
•
•
All cells are surrounded by a plasma membrane (cell
membrane) which is selectively permeable to
materials.
Prokaryotes lack a true nucleus as well as internal
membrane-bound organelles.
–
•
Bacteria
Eukaryotes have a true nucleus and have at least one
membrane-bound organelle
–
Include plant, animal, fungi, protozoa and algae cells
CELL SIZE
•
•
•
Prokaryotic cells can be
1-10 μm, while
eukaryotic cells are 10100 μm.
Some eukaryotic cells
are quite large, like the
yolk of a chicken egg
Two organelles found in
eukaryotes, the
mitochondrion and the
chloroplast, are similar
in size to most bacteria.
CELL SIZE

The ratio of surface area to cell volume limits cell
size because it reflects the balance between
supply rate and supply demand.


The surface area determines the rate at which
materials diffuse into or out of the cell.
For a cell of a constant shape, for every time the
surface area increases by L2, volume increases L3
PROKARYOTES
•
•
•
•
Prokaryotes have no true
nucleus or membranebound organelles, have a
nucleoid region
Has a Cell Wall, and
some may have a
capsule, which encloses
the cell wall
Forms of movement are
the flagella and/or the
pilli
Contains ribosomes
where protein synthesis
occurs
PROKARYOTES

Bacteria cells have
different shapes
Rod-shape
 Spherical shape
 Spiral

EUKARYOTES

Eukaryotes, unlike prokaryotes, have a true,
membrane-bound nucleus.

Contain a variety of organelles, specialized
membrane-bound structures where cell processes
occur
ENDOPLASMIC RETICULUM
•
Endoplasmic Reticulum
(ER) is where proteins
and lipids are
synthesized
Large surface area
– Rough ER is embedded
with ribosomes
–
•
–
Ribosomes are
nonmembranous organelles
that help with synthesis of
proteins
Smooth ER is where
lipids are synthesized,
detox
GOLGI APPARATUS

Golgi Apparatus are
smooth, flattened
membranous sacs
Collects, packages and
distributes molecules
manufactured in the
cell
 Animals contain
around 20 complexes,
plants have hundreds.

VESICLES AND VACUOLES
•
Tiny, membranous sacs known as vesicles deliver
molecules to and from the Golgi Complex, vacuoles are
larger structures that perform the same tasks
Some go from ER to the Golgi Complex
– Some go to other organelles in cell
– Others will go to plasma membrane and combine with it
–
•
•
–
May contain insulin, enzymes, etc. to go outside the cell
In plants, some vesicles have cellulose to make new cell wall
material
Some vesicles contain enzymes to breakdown various
molecules
LYSOSOME

A lysosome is a tiny vesicle
that buds off the Golgi
Apparatus and contains
enzymes that break down
macromolecules, for
digestion and destruction

These enzymes function
best at a pH of 5


Hydrogen ions are
transported into lysosome to
create this acidic
environment
Will also destroy bacteria,
viruses and fungi
Fig.
4.11, pg.
77.
PEROXISOME

A peroxisome is an organelle that has the
enzyme, catalase, that breaks down hydrogen
peroxide, H2O2
Breaks down fatty acids into 2 carbon fragments
 n addition it includes enzymes which synthesize
cholesterol and bile acids.

Is not formed in the Golgi apparatus
 Aids chemical reactions, including the breakdown
of fatty acids, synthesis of cholesterol and
synthesis of lipid molecules

RIBOSOMES



Ribosomes are constructed
from two subunits, which
are composed of ribosomal
RNA and proteins.
Ribosomes synthesize
polypeptides from free
amino acids, according to
the instructions on
messenger RNA.
Ribosomes are like CD
players, producing music
(proteins) according to the
instructions on the CD
(mRNA).
NUCLEUS
The nucleus is
surrounded by two
membranes, the
nuclear envelope
 Protein complexes at
nuclear pores regulate
the entry of large
macromolecules into
and out of the nucleus
 The nucleus contains
most of the DNA in a
cell.

NUCLEUS
The primary function
of the nucleus is to
transfer the
information for the
synthesis of proteins
from DNA to RNA.
 The nucleolus is a
dense area within the
nucleus with DNA
fragments, ribosomal
RNA, and proteins.
 The nucleolus
organizes the RNA
and proteins into the
ribosomal subunits.

MITOCHONDRIA
Mitochondrion
(singular) has two
membranes
 Outer membrane is
relatively simple, but
the inner membrane is
highly folded, a
structure called cristae
 Cristae are rich in
enzymes for electron
transfer and ATP
synthesis

MITOCHONDRIA
The matrix is a fluid
filled space inside the
inner membrane
 It contains soluble
enzymes for aerobic
cellular respiration.
 The matrix also
contains DNA
(mtDNA), RNA, and
ribosomes.

MITOCHONDRIA
Known as the powerhouse of the cell
 It converts the energy stored in organic molecules
to forms usable to the cells, especially production
of ATP
 Food + O2 → CO2 +H20 + Energy (ATP)

CHLOROPLASTS
Chloroplasts are also surrounded by two membranes.
 The outer and inner membranes, and intermembrane
space are barriers, but play no specific functional role in
photosynthesis.
 Inside the inner membrane is the stroma, an aqueous
space.
 Floating in the stroma are thylakoids, flat membranous
sac.

CHLOROPLASTS
The thylakoid membrane contains chlorophyll
and other pigments, electron transfer molecules,
and enzymes that trap the energy in sunlight photosynthesis.
 This energy is used to generate ATP and high
energy electrons in the light-dependent phase of
photosynthesis.
 These molecules pass to the stroma where CO2
and H2O are converted into sugars.

CHLOROPLASTS
The stroma also contains DNA (chDNA), RNA,
and ribosomes.
 In the stroma, DNA is transcribed to RNA and
RNA is translated into some chloroplast proteins.

CYTOSKELETON



Intermediate filaments are semi-permanent
components of the cytoskeleton.
Intermediate filaments are semi-permanent
components of the cytoskeleton.
Intermediate filaments maintain cell shape and
attach to proteins in the cell membrane
CYTOSKELETON

Microfilaments are built with the beadlike protein
actin
During cell division, motor proteins pull actin filaments
together, slicing the cytoplasm in half like string
around a ball of dough.
 In muscle cells, the motor protein myosin pulls

CYTOSKELETON


Microtubules are small tubes that are built with the
protein tubulin.
During normal conditions, one of their functions is to
act as roadways for motor proteins.
CYTOSKELETON
Microtubules are also
the central supports
for cilia and flagella.
 Covered by just the
cell membrane, cilia
and flagella extend
from the cell.
 Motor proteins
push/pull on the
tubules within the
cilium/flagellum.
 This causes them to
move back and forth.

CELL MEMBRANES
Phospholipids are the
dominant molecule in
membranes.
 Phospholipids
naturally assemble
into a bilayer
 The membrane’s
center is hydrophobic
because of the fatty
acid tails.
 The outer edges are
hydrophilic because of
the phosphate groups.

FLUID MOSAIC OF MEMBRANES
CELL TRANSPORT




A membrane is a selectively permeable barrier
Single molecules that are nonpolar or only slightly polar can pass
through the hydrophobic core without problems.
These include O2, N2, CO2, steroids, alcohols, fatty acids, and
pesticides.
The cell cannot regulate movement of these molecules as they follow
the rules of simple diffusion
CELL TRANSPORT
Single molecules that are polar or charged
require a transport protein or channel protein to
pass through the core.
 These include H20, ions, sugars, amino acids, and
proteins.
 Their movements
into / out of the cell
can be regulated by
modifying the
proteins involved.

CELLTRANSPORT

Materials can move pass membranes:

A) as single molecules (diffusion and active transport)
or in large quantities (vesicular transport)

B) without input of energy (passive transport) or
requiring energy (active transport)

C) without the help of a protein (simple diffusion) or
with the help of a protein (facilitated and channelmediated diffusion).
DIFFUSION


During diffusion, molecules move from areas of
higher concentration to areas of lower
concentration, “down” the concentration gradient.
At equilibrium, movements of molecules in one
direction are balanced by movements in the
opposite direction.
DIFFUSION

Diffusion rates depend on:

a) the distance over which molecules must move:


b) the size of the molecule:


wider = faster
d) the speed that molecules are moving =
temperature:


smaller = faster
c) the surface available for diffusion:


shorter (thinner membrane) = faster
higher = faster
e) the concentration gradient between two points

greater concentration difference = faster.
DIFFUSION
Diffusion rates also depend on how permeable
the membrane is to a particular kind of molecule
 The diffusion rates of one type of molecule are
independent of the concentrations of any other
types of molecules
 In simple diffusion, molecules move
past the membrane through the lipid
core.

DIFFUSION

In channel mediated diffusion, molecules pass
the membrane through a protein pore.
OSMOSIS

Osmosis is the movement of “free” water down its
concentration gradient.
Some water molecules surround solutes as part of
spheres of hydration.
 If a membrane is not permeable to that solute,
then these water molecules cannot pass either.
 A solution with few dissolved molecules (low
osmolarity) will have more free water molecules
than a solution with more dissolved molecules
(high osmolarity).

OSMOSIS



Imagine that we have a
selectively permeable
membrane separating a
40% sugar solution from a
10% sugar solution.
There are more “free”
water molecules on the
10% sugar side than there
are on the 40% sugar side.
Because there are more
“free” water molecules in
the 10% side, water will
move by osmosis (diffusion
of water) to the 40% side.
ISOTONIC

If the concentration of dissolved materials is
equal in the surrounding solution as in the cell,
then no net movement of water occurs.
HYPERTONIC


If the concentration of dissolved materials is greater in
the solution than in the cell, then water will leave the
cell. The solution is hypertonic compared to the cell.
If the concentration of dissolved materials is lower in
the solution than in the cell, then water will enter the
cell. The solution is hypotonic compared to the cell.
TRANSPORT
Specific carrier proteins
allow materials that are not
hydrophobic to pass through
a membrane.
 In facilitated diffusion, the
carrier protein allows
molecules to move from high
concentration to low
concentration.
 Osmosis, facilitated
diffusion, and standard
diffusion are all examples of
passive transport.


movement of materials down a
concentration gradient without
expenditure of energy
ACTIVE TRANPSORT
Active transport is the movement of materials
across a membrane against its concentration
gradient.
 Molecules are pumped from low concentration to
higher concentration.
 Active transport requires metabolic energy to do
the pumping.

In exocytosis a membrane-bound sac (a vesicle)
fuses with a membrane and dumps the fluid
contents outside the membrane (usually outside
the cell).
 Endocytosis is the reverse of exocytosis.


A region of membrane forms a pocket around the
external materials, pinches off a vesicle, and
transports this material inside.
In phagocytosis, the materials being brought
insides are solid particles.
 In pinocytosis, the materials being brought inside
are fluids.

ENDOCYTOSIS AND EXOCYTOSIS
White blood cells actively use endocytosis and
exocytosis in their role as defenders of the body
from invaders.
 When they detect a microbe, they extend fingers
of membrane and cytoplasm to surround it.
 When the membrane fingers meet, they fuse.
