Download Cell Membrane - Saint Joseph High School

Cells
How do we look at cells?
• Most cells are too small to see with the
naked eye, so how do we see them?
• Just how small is too small?
Microscope Power Line
Compound Light Microscope
• Uses 1 or more
lenses to produce
enlarged images
• Allows you to see
living cells
• Magnifies up to
2,000 times
Electron Microscopes
• Use beams of electrons,
similar to your television
• Can’t see living cells,
because specimens are
put into a vacuum
• Magnifies up to 200,000
times
• 2 types
Transmission Electron Microscope
• Thin slices stained with metal ions
• Heavily stained portions absorb electrons
• Lightly stained portions the electrons pass
through, hitting a fluorescent screen and
forming an image
• Black and white images, color added
Scanning Electron Microscope
• Coated with layer of
metal
• Electrons bounce off
onto a fluorescent
screen
• 3-D black and white
images, color added
Scanning Tunneling Microscope
• Uses voltage differences
to create digital images
• Allows you to see
individual atoms in 3-D
• You can see living
organisms
• Magnifies up to 10
million times
Cell Theory
1. All living things are made of one or
more cells
2. Cells are the basic units of structure and
function in organisms
3. All cells arise from existing cells
What is a cell?
• All cells have all of the equipment
necessary to perform the essential
functions of life
• All cells share several common features
• There are 2 types of cells
What features do all cells share?
• Cell membrane—the outer boundary that
encloses the cell, protects it from its
surroundings, and regulates what leave and
enters, including gases, nutrients, and wastes
• Cytoplasm—the cell interior
• Ribosomes—the place where proteins are
made
• DNA—provides instructions
What are the two types of cells?
Prokaryotes
Eukaryotes
Prokaryotes
• The smallest and simplest cells, 1 – 15
µm
• Lack a nucleus and other internal
compartments
• Lived at least 3.5 billion years ago
• An example is a bacteria
Characteristics of Prokaryotes
•
•
•
•
Grow and divide rapidly
Some need O2, others don’t
Some make their own food
No internal compartments, so enzymes
and ribosomes move about freely
• Single, circular strand of DNA
• Cell wall
Prokaryotic Cell Wall
• The cell wall is made of polysaccharides
with short amino acid chains attached
• Prokaryotes have to have a cell wall,
because they do not have an internal
skeleton
–A prokaryote’s cell wall is to a bacteria
as an insect’s exoskeleton is to an ant
Prokaryotes’ Capsules
• Some prokaryotes have capsules out side
of their cell walls
• Allow them to cling to almost anything,
like skin, teeth, and food
• How would this benefit them?
Flagella
• Many prokaryotes have
flagella, long threadlike
structure that protrude
from the cell’s surface and
enable movement
• The flagella rotate to propel
the prokaryote
Eukaryotes
• Any organisms whose
cells have a nucleus
• They also have other
internal compartments,
called organelles
• Evolved about 1.5
billion years ago
Nucleus, Organelles, and
Cytoplasm
• The nucleus is an internal compartment
that houses the cell’s DNA
• Organelles are other internal structures
that carry out specific functions in the
cell
• Cytoplasm is everything inside the
cell membrane but outside the
nucleus
Flagella and Cilia
•Cilia are short, hair-like
structures that protrude from
cell surfaces
•Flagella and cilia can propel cells
or they can move substances
across a cell’s surface
•Cilia in lungs sweep mucus and
debris away and in your ears they
conduct sound vibrations
Cytoskeleton
• The cytoskeleton is a web of protein fibers
• It holds the cell together and keeps cell
membranes from collapsing
• Anchored to cell membrane
• It links one region to another
• Anchors nucleus and organelles to fixed
locations
• 3 different kinds—microfilaments,
microtubules, and intermediate filaments
Microfilaments
• Long and slender, made of actin
• Network beneath cell’s surface that is
anchored to the membrane proteins
• Determines the shape of the cell
Microtubules
• Hollow tubes of tubulin
• Within the cytoskeleton, microtubules
act as the highway for transportation of
information from the nucleus out
• RNA/protein complexes are transported
along the “tracks” of microtubules by
motor proteins
Intermediate Filaments
• Intermediate filaments are thick ropes of
protein
• They make up the frame that allows
ribosomes and enzymes to be confined,
which allows cells to organize complex
metabolic activities
efficiently
Cell Membrane
• Cell membranes are made up of
phospholipids, which are a phosphate
group and two fatty acids
• Phospholipids are made up of a polar
“head” and two nonpolar “tails”
• Phospholipids form a phospholipid
bilayer
Cell Membrane
• Cell membranes have selective permeability
• The lipid bilayer allows lipids and substances
that dissolve in lipids to pass through
• Membrane proteins are also part of the
membrane—some are for transport
Cell Membrane
• There are several types of membrane
proteins, including:
– Marker proteins
– Transport proteins
– Enzymes
– Receptor proteins
• Proteins move, because phospholipids
are constantly in motion
Nucleus
• Houses most of the DNA, which controls
the cell’s functions
• Surrounded by a double membrane,
called the nuclear envelope or nuclear
membrane
• The nuclear envelope is made of two
lipid bilayers
• Why do you think that there are 2?
Nucleus
• Nuclear pores are small channels through
the nuclear envelope
• What are the pores for?
• The nucleolus is an area of the nucleus
where ribosomes are partially assembled
• Eukaryotic DNA is tightly wound around
proteins, and appears as a dark mass under
magnification most of the time
Ribosomes
• Made up of dozens of proteins and RNA
• Cells make proteins on ribosomes
• Some are suspended in the cytosol. These
are “free” ribosomes. “Free” ribosomes
make proteins that remain in the cell.
• Proteins that leave the cell are made on
ribosomes on the surface of the
endoplasmic reticulum
Endoplasmic Reticulum
• An extensive system of internal
membranes that move proteins and
other substances through the cell
• The membrane of ER is a lipid bilayer
with embedded
proteins
Rough Endoplasmic Reticulum
• The Rough ER has ribosomes attached
–It helps transport proteins made on the
attached ribosomes
–The proteins enter the ER and a small,
membrane-bound sac, or vesicle, pinches
off
–Proteins made on ribosomes on
the rough ER stay separate from
proteins made on free ribosomes
Smooth Endoplasmic Reticulum
• The Smooth
Endoplasmic Reticulum
lacks ribosomes, so it
appears smooth under
an electron microscope
• The smooth ER makes
lipids and breaks down
toxic substances
Golgi Apparatus
• A flattened, membranebound sac that serves as
the packaging and
distribution center of
the cell
• Enzymes in the Golgi
Apparatus modify
proteins from the ER
Lysosomes
• Lysosomes are small, spherical organelles
that contain the cell’s digestive enzymes
Mitochondria
• Organelle that uses
organic compounds to
make ATP, the primary
energy source of cells
• Cells with high energy
requirements, like
muscle cells, may contain
hundreds or thousands
or mitochondria
Mitochondria
• The mitochondria has two membranes
–The outer membrane is smooth
–The inner membrane is greatly folded, so
that it has a lot of surface area
–The two membranes
form two compartments
Mitochondria
• The mitochondria also
contain DNA and
ribosomes, because they
make some of their own
proteins
• Most mitochondrial
proteins are made in the
cytosol
Organelles Only Found in Plants
• Plants have 3
unique organelles
–Cell wall
–Chloroplasts
–Central vacuole
Cell Wall
• Plants’ cell membranes are surrounded by
cell walls
• Plant cell walls are made of proteins and
carbohydrates, including cellulose
• Helps support and protect the cells
• Connects cells to one another
Chloroplasts
• Chloroplasts are organelles that use light to
make carbohydrates from CO2 and H2O
• Found in algae as well as plants
• Surrounded by 2 membranes
• Contain their own DNA
Central Vacuole
•
•
•
•
The central vacuole stores water
It may contain ions, nutrients, and wastes
It makes the cell rigid, when it is full
Enables plants to stand upright
Let’s Review
• We use microscopes to look at cells that
are too small to see with the naked eye
• The Cell Theory
• What is a cell? What do all cells share?
• Prokaryotes vs. Eukaryotes
• Nucleus, Organelles, and Cytoplasm, oh
my!
• What separates plants from other
eukaryotes?
The Cell
contains
Cytoplasm
1.
Function as
Ribosomes
Function as
3.
ER & Golgi
apparatus
Function as
4.
5.
Function as
Support/
structure
6.
Function as
Power
Plants
2.
How did eukaryotes and
prokaryotes come to be so
different?
Lynn Margulis
Margulis’s Other Causal Questions
• Why do mitochondria and chloroplasts
have their own DNA?
• Why do they have two membranes,
when other organelles only have one?
• Why do these organelles reproduce
separately from the rest of the cell?
Endosymbiont Theory
• Margulis proposed that billions of years
ago, eukaryotic cells arose as a
combination of different prokaryotic cells
• The ancestors of mitochondria and
chloroplasts were once symbionts living
inside larger cells
• They eventually lost their independence
and became organelles
Endosymbiont Theory
• The theory answered each of Margulis’s
questions
– They have their own DNA and reproduce
separately because they were once
independent
– The inner membrane could be a remnant of
the old cell membrane and the outer
membrane could be the cell’s membrane
surrounding the “foreign cell”
– Further evidence supports Margulis’s Theory
Why aren’t organisms made of a
few large cells?
• The human body is made up of about
100 trillion cells
• Most of our cells are from 5µm - 20µm in
diameter
(There are 100 µm in 1 mm)
Surface Area-to-Volume Ratios
1. Calculate the surface area-tovolume ratio of a cube with a
side length of 2mm.
2. Calculate the surface area-tovolume ratio of a cube with a
side length of 1mm.
Relationship Between Surface Area
and Volume
Side Length Surface
area
Volume
1 mm
6 mm2
1 mm3
Surface
area :
volume
ratio
6:1
2 mm
24 mm2
8 mm3
3:1
4 mm
96 mm2
64 mm3
3:2
Why would the surface area to
volume ratio be important?
• How does the flatness of a single-celled
Paramecium affect the cell’s surface area-tovolume ratio?
• How would it affect the
cell’s ability to survive?