The Cell: Structures and their Function (see sections 2.2 and 2.3 in Probe 9)
Cell Membrane
 the membrane is made from fats and proteins
 provides structure and support to the cell
 it is the “gate keeper”, controls movement into and out of the cell by a variety of means
Cytoplasm
 thin jelly-like substance where all cell activities occur.
 gives the cell structure
 made mostly of water and dissolved substances, plus all organelles
Endoplasmic Reticulum (ER)
 a series of connected canals that are found attached with the nuclear membrane
 produce fats and fat soluble hormones if no ribosomes attached (SER)
 produce proteins if ribosomes are attached (RER)
 move substances in cells by packaging products in vesicles
Ribosomes
 protein factories
 found mainly on the ER, but also found floating free in the cytoplasm
Vacuoles
 multipurpose sac made from cell membrane that can be used for a variety of purposes
 intake of food, digestion, and excretion
 removal of excess water
 carry enzymes, hormones, etc. to be used by the cell OR exported outside the cell
 LARGE IN PLANT CELLS, small in animal cells.
Nucleus
 Contains DNA (deoxyribonucleic acid)
 control center of the cell, DNA controls
all chemical reactions and activities in a
cell by controlling the production of
ENZYMES. DNA is the blueprint for enzymes.
 Contains pores in its membrane through which certain materials are
allowed in and out.
Nucleolus
 found INSIDE the nucleus
 doesn’t have a membrane
 makes ribosomes which then pass out through the nuclear membrane.
Chromosomes or DNA
 long thread-like molecules made of units called
nucleotides
 humans have 46 chromosomes in our body cells, (or
23 PAIRS)
 each molecule of DNA contains codes for thousands
of proteins.
 a gene is a short section of DNA that contains instructions to make a specific
protein.
 one gene codes for one protein
 Enzymes are proteins!
THE DNA MOLECULE
 DNA is stored as chromatin in the nucleus
 long (like, REALLY long)
 double- helix
 one strand contains thousands of genes
 each gene codes for only one protein
 Made of a sugar-phosphate backbone
 Has Nitrogenous bases
 Bases held together by hydrogen bonds.
Nucleotides
 sub-units that make up DNA
 Contain a sugar-phosphate 'backbone, and
one of 4 'nitrogenous' bases

adenine (A)

guanine (G)

cytosine (C)

thymine (T)
 thousands of nucleotides linked together make a gene
 adenine always pairs with thymine, guanine pairs with
cytosine in DNA, (slightly different in RNA, a molecule involved in making proteins)
 3 nucleotides make the code for one amino acid (one unit of a protein). This code is called a
codon. In the above example, ACG is a codon, followed by TAC in the TOP part of this
DNA molecule. The COMPLEMENTARY codons (codons on the other side) are TGC and
ATG
 There are 20 different amino acids in the body, 12 are made by your body. Eight of them
you cannot make and must get them in your diet.
You do NOT have to know this
table! This table just shows you the
codes for amino acids. Notice some
of them say STOP. That is because
the ribosome needs to know when
the protein is finished, so the codon
tells it to stop making the protein.
Any change in one base in the DNA molecule (a mutation) can cause a protein to be changed
enough that it does not function: This can cause a genetic disease!
How proteins are Made
(see page 44 in your text)
 Proteins are like any building toys, you
stick smaller units together to make
bigger units.
 The nucleus receives a signal to make
a specific protein. For instance, you
might have eaten a big bag of M&Ms
and you need to make some insulin to
get rid of all the sugar in your blood
stream. The nucleus has the
instructions to make insulin and the high blood sugar signal would get the nucleus to make
insulin.
 DNA transfers the instructions to make the protein, like insulin, to a messenger molecule
called messenger RNA, or mRNA.
 mRNA takes these instructions (the message) out of the nucleus (through a nuclear pore) to
a ribosome, usually located on the rough endoplasmic reticulum.
 The ribosome reads the codons on the mRNA and adds the appropriate amino acid to the
growing protein chain.
 When the protein is complete, it goes through the endoplasmic reticulum until it reaches the
end, and then it is packaged in a vesicle and sent to the Golgi body.
 The Golgi body repackages the protein in another vesicle and ships it to the cell membrane.
 The vesicle becomes part of the cell membrane as it dumps the protein to outside the cell.
 In the case of insulin it would be dumped into the blood stream and would tell the cells of
your liver to store the sugar as glycogen.