cell membrane

twoeggfinnishBiotechnology

Dec 14, 2012 (4 years and 6 months ago)

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Cell Structures and
Functions (Eukaryotic
Cells) Notes

Mrs. Linde

Biology 1

Points to consider:


We will organize
structures

into groups
according to overall
functions

that
occur in the cell


We will concentrate on the function of
maintaining homeostasis


Each
organelle

has a specific job.


All parts of the cell work
together

to
help the cell to
survive

and
grow
.

I. Organelles that serve as
Boundaries/Support Structures

A.
Cell Membrane


1. Found in both
plant

and
animal

cells.


2. In order to
survive
, a cell must be able
to respond to needs both
inside

and
outside

of the cell while keeping the
environment inside the cell
balanced
. If a
cell can successfully do these things, it
maintains
homeostasis
.

3.
One of the cell membrane’s functions =
let in
proper amounts of
glucose

(for
energy
),
amino acids

(for
protein synthesis
), and fats
(
lipids
).

If a cell has too much or too little of
any of these
molecules

or if a cell has
excess
waste

that it can’t get rid of, the cell could
die. When would this death be a good thing?
With cancer cells


Picture 1:

4.
How does the membrane work in order to
maintain homeostasis inside of the cell?


Answer:
by being semi
-
permeable
. What
does this mean?


Picture 2:

A screen door is semi
-
permeable; it lets some
things in (air), it lets some
things out (pets), it keeps
some things in (toddlers), it
keeps some things out
(bugs), it lets some things
in and out (people)

5.
However
, the cell membrane does not look like
a screen

it looks like this
:




Picture 3:

6. Cell Membrane Structure



a. The cell membrane is made of
2

layers. Each
layer is made of a fat (
diglyceride
) with a
phosphate

group bonded to it.







Picture 4:


b. The cell membrane is said to be a
selectively permeable membrane
.




c. Look how the phospholipids arrange
themselves to make the cell membrane. The
fatty acids

align themselves so that they are
inside the membrane
. The phosphate groups
are pointed towards the
inside

and the
outside

of the cell.



d. Why do the fat and phosphate align
themselves like this? Answer:
water

(which is
a polar molecule) is found inside and outside
of the cell.
Phosphate

groups are also polar.
Polar things are attracted to
each other
. That
is why the tails (fats = nonpolar) and
phosphate groups line up like they do and not
like this…


Picture:

7. Other components of the cell membrane

a.
Protein molecules

1.
Transport Proteins


used as
channel
s through
which
waste

and certain types of molecules must
pass through in order to get
in

and
out

of the cell
.


2.
Identifying
Proteins


help to identify the cell as
being a certain type of cell and helps cells to
recognize each other.

a. In terms of the
medical field

and
genetic engineering
, these
proteins are
very

important.

blue

orange



3.
Inner surface proteins


help to attach




the
cell membrane

to the cell’s
inner




skeleton
, helping to give a cell its




flexibility
.


b.
Carbohydrate

Molecules


help cells to



identify

each other and protect cells from



infection.

green

black


c.
Cholesterol



1. Prevents the
fatty acid

chains of the




phospholipid

bilayer

from sticking



together
.



2. Plays an important role in the
stability

of




the
cell membrane

purple

I. Organelles that serve as
Boundaries/Support Structures

B. Cell
Wall



1. Found in
plant

or
prokaryotic
cells only


2.
The cell wall works as a rigid barrier that protects
the plant cell and gives it shape.


Picture:

B. Cell Wall


3. The cell wall is made out of a




carbohydrate

named
cellulose
.


4. It is very
porous
, but unlike the cell
membrane
, it does not
decide

which
molecules can
enter

and
exit
the cell.

C. Cytoplasm


the clear, gelatinous liquid


inside of a cell
that holds the cell together




II. Cellular
Control



A. Nucleus


1. Every part of the cell depends on the
nucleus

to
do its job.
The nucleus contains the DNA/
blueprints on how to make proteins; therefore, the
nucleus is in charge of what happens in a cell
. You
could think of the nucleus as being the
brain

of the
cell.

B. Nuclear Membrane/
Envelope


1.
The nuclear membrane serves to
separate the inside of the nucleus from the
rest of the cell
.


2. The nuclear membrane is composed of a
phospholipid
bilayer
.



3. The nuclear membrane is full of
pores
.
These pores allow substances to pass through
.
Structures called mRNA, which contain the
instructions for which
proteins

should be
made in the cell, will need to move through
the pores and move to the ribosomes.


Picture:


C. Nucleolus



1. Under the microscope, this appears
as a
dark

round structure in the
nucleus
.


2.
Ribosomes are made in the
nucleolus
. Once they are made, the
ribosomes will pass through a
nuclear
pore

to the cytoplasm. (Picture 3)




D. Chromosomes/Chromatin


strands of
genetic/hereditary material made up of


DNA and protein
that makes us who we are

E. Ribosomes


1. Ribosomes are small, dense organelles that are present in
great numbers in the cell.


2.
Proteins are made on the ribosome
. Proteins are made of
amino acid

molecules bonded together. On the ribosomes,
amino acids bond together at a rate of

20

AA per second. The


average
-
sized protein takes
150

seconds to make.

III.Assembly, Transport, and Storage


Perhaps you have figured out by now that
making proteins is one of the cell’s main
functions
. You should know by this point that
the
nucleus

chromosomes

DNA

hold the
message about which proteins should be
made. And, you know that this message has
to get out of the nucleus and to the
ribosomes
, where proteins are made.

A. Endoplasmic Reticulum (ER)


1. The ER is a series of
interconnected
flattened tubular
channels

which are continuous


with the
nuclear membrane
. The ER can take up a lot of
space

in the cell.


2. Two types of ER:



a.
Smooth

ER


not covered in this class


b.
Rough

ER


appears ‘rough’ because it


has
ribosomes

attached to its
surface
.

3. The rough ER
takes in the proteins made on the ribosome
into a place called the cisternal space so that they do not
escape
into

the cytoplasm until the proteins are completely
formed. In here, the proteins can fold up into their specific
3
-
D form
.

4. Small
vesicles

containing newly made
proteins
pinch off from
the ends of the
ER
and either join with the
golgi body

or
perhaps leave the
cell
.



5. Each
protein

made in the rough ER has a
particular
function
; it may become the protein
that forms part of the
cell membrane
, or it
may be a protein that is released from the cell
that has a
job

to do elsewhere in the
body
.

B. Golgi Body



1. The golgi body is a flattened system of tubular
membranes that modify proteins and fats by, for
example, attaching sugar molecules on them to
form glycoproteins and glycolipids.


2.
The golgi body sorts the proteins (made in the
cell) into packages (vesicles) to be sent to the
correct destination.


3. Located near the ER.



Picture 1:

Protein (x)

Golgi body

X

Vesicle

C. Vesicles



1. Vesicles just like the golgi body
modify
proteins that are made in the cell on the
ribosomes.

D. Vacuoles



1. A vacuole is a sac surrounded by a vacular
membrane



2.
Vacuoles store food, enzymes, and other
materials needed by the cell. Sometimes they
store waste products.


3. Plant cells usually have 1 big vacuole,
whereas animal cells have many little
vacuoles.


Picture 2:


Vacuole




Vacular







Membrane



Picture:

E. Vacular membrane



1. The vacular membrane
allows molecules to
pass in and out of the vacuole.

F. Pinocytic vesicles



1. The pinocytic vessicle is a
structure that is
used for bulk transport

(type of active
transport)

for example, endocytosis and
exocytosis.


Picture 3:


G. Lysosomes


o
rganelles that contain
digestive enzymes. These enzymes
digest
(break down) extra or worn out organelles and
bacteria

that have entered the cell.


White stuff =

Digestive enzymes

IV. Energy Producers

We have talked about several organelles and
their function in the cell. Organelles require
energy to get their jobs done. Making
proteins, transporting proteins and other
molecules, and digesting things in the cell all
require energy.

A. Mitochondria



1. The mitochondria is an organelle found in
both plant and animal cells.



2. Energy in a form that can be used by the
cell is produced in the mitochondria. The
name of this process is cellular respiration.
This is a complicated process, but here is what
happens…




Cellular Respiration =

C
6
H
12
O
6

+ 0
2

= CO
2

+ H
2
O + ATP

Glucose Oxygen Carbon Water Energy


Dioxide



3. Mitochondria are small organelles. Most
cells contain many mitochondria.


B. Cristae



1. The inside membrane of the mitochondria.



2.
The cristae gives more surface area

for the
attachment of some structures involved in the
process by which cells get energy = cellular
respiration

C. Chloroplast



1. The chloroplast is an organelle found
only in plant cells


Thalkaloid

Membrane




Chloroplast




2. Chloroplasts are organelles that
capture
light energy and use it to produce glucose
,
which then is used by the plant for energy.

V. Miscellaneous Structures

A. Centrioles


1. Centrioles are structures that
come into
play when the cell is undergoing mitosis

(which means the cell is dividing into two
new cells).


Picture:

B. Microtubules



1. Microtubules are cylinders of protein.
Microtubules
help organelles and other things
(like chromosomes) move from place to place
in the cell
.

VI. Cellular Components

A. Let’s take a look at a typical human liver cell’s components:



Organelle

% of total cell
volume

Approximate
number per cell

Cytoplasm

54%

1

Mitochondria

22%

1700

Rough ER

9%

1

Smooth ER

6%

1

Nucleus

6%

1

Lysosomes

1%

300

B. Keep these numbers in mind when you draw
cells!