1. How did mitochondria form? How does it divide within cell? What is its major function?
Mitchondria arose from the process of phagocytosis of an aerobic prokaryote. It can
divide in the cell using a process called “mitochondrial fission” - powerhouse of the
cell. Mitochondria’s major function is aerobic respiration.
Aerobic respiration is utilizing oxygen to extract energy from macromolecules
(primarily glucose) and converting it into ATP
Thus mitochondria is key for ATP production
2. What does the following Figure 5.1 Mitochrondria show?
a. A living fibroblast viewed with a phase-contrast microscope. Mitochondria are seen
as elongated, dark bodies
b. Transmission electron micrograph of a thin section through a mitochondrion
revealing the internal structure of the organelle, particularly the membranous cristae
of the inner membrane.
c. Localization of mitochondria in the sperm midpiece surrounding the proximal portion
of the flagellum (Bright-field +stain microscope)
3. How do humans make benefit from having mitochondria?
Humans use 2 x 10 molecules of ATP per day. ATP is a cells energy source and the
energy is released when ATP is hydrolyzed to ADP.
Also many mitochondria can be found with the: muscle cells, liver cells, fat cells,
plant cells, and even sperm
4. How does the mitochondria’s structure look?
The mitochondria consists of the:
I. Outer membrane
II. Inter-membrane space (found between the outer/inner membrane)
III. Inner membrane (cristae) which has a high surface area = more ATP produced
IV. Matrix which is the space in which the Kreb’s cycle occurs Mitochondria. Schematic diagrams showing the
Figure 5.3 - The structure of the mitochondria. three-dimensional internal structure (top) and a
Scanning the internal matrix enclosed by folds of the thin section (bottom) of a mitochondrion from
inner membrane bovine heart tissue.
5. What is the purpose of the outer mitochondrial membrane (OMM)?
The OMM is 50% protein: 50% lipid ratio
It contains porin proteins which are bacteria proteins with large channels that
allow very large molecules through the cell
Figure 5.4 – Porins. Gram-negative bacteria
have a lipid-containing outer membrane outside
of their plasma membrane as part of their cell
wall. This outer membrane contains proteins,
called porins, which consist of a barrel of B sheet
and form an opening through which moderate-
sized molecules can penetrate. This image shows
OmpW embedded in the outer membrane of
compound within its central channel. A variety
of porins having different sized channels and
selectivity’s are also found in the outer
mitochondrial membrane in eukaryotic cells
6. What is the purpose of the inner mitochondrial membrane (IMM)?
The IMM can also be called the cristae which are the many thin folds to increase
surface area of the mitochondria
It has a 75% protein: 25% lipid ratio
Lipid in IMM refers to the cardiolipin which is a unique phospholipid also
found in many bacterial membranes; IMM has more proteins than the outer
The IMM is very impermeable and it requires channels and pumps for movement across
There are 100 different proteins which include the proteins of the ETC
7. What is the purpose of the matrix within the mitochondria?
The matrix is gel-like from high protein concentration
It contains DNA, ribosomes, and tRNA
The mitochondrial DNA encodes for 37 genes, however, mitochondrial function
requires a sum of 3,000 proteins Therefore mitochondria function requires nuclear gene products, and these
proteins must be imported (targeted) to the mitochondria
Protein translocons are also involved in import of proteins into the
Mitochondria proteins are completely translated on free ribosomes with the
8. The posttranslational uptake of protein into mitochondria - What is the targeting
sequence of mitochondrial proteins?
a. Mitochondrial “presequence” – which occurs at the amino terminus of
“preprotein” with several positively charged amino acids – for soluble matrix
b. Internal sequence and stop transfer sequence – for integral IMM proteins
9. What are the proposed steps of importing proteins into a mitochondrion?
Figure 8.47 – Importing proteins into mitochondria.
1. The polypeptide is targeted to a mitochondrion by a targeting sequence, which is
most inner membrane proteins (step A).x proteins (step1) and is located internally in
2. Cytosolic Hsp70 molecules unfold the polypeptides prior to their entry into the
mitochondrion. The proteins are recognized by membrane receptors and
translocate through the OMM by way of pores in the TOM complex of the OMM
(step 2 or B).
3. Most integral proteins of the IMM are directed to the TIM22 complex of the IMM
Mitochondrial matrix proteins are translocated through the TIM23 complex of the
IMM (step3). Once the protein enters the matrix, it is bound by a mitochondrial
chaperone (step4), which may either pull the polypeptide into the matrix or act
like a Brownian ratchet to ensure that is diffuses into the matrix.
4. Once in the matrix, the unfolded protein assumes its native conformation (step5a)
with the help of Hsp60 chaperones. The presequence is removed enzymatically
10.How do you import proteins into the mitochondria through outer membrane?
In order to enter the mitochondria:
a) Protein is first unfolded by the Hsp70 – chaperone protein
b) The protein then binds to its receptor on OMM – outer mitochondrial membrane
which is located next to a translocon on OMM which is called the TOM
(translocon of outer membrane)
11.How do you import proteins into mitochondria when it is within the inner membrane?
IMM intergral proteins are directed to the TIM22 complex of IMM
a) Thus protein is directed to TIM22
b) TIM (translocon of inner membrane) then stops transfer sequence and embeds
protein in the IMM; this includes all proteins of the ETP and the ATP synthase
12.How do you import proteins in mitochondria when it is destined for the matrix?
Matrix proteins are directed to TIM23 complex of the IMM
a) Thus protein directed to TIM23
b) A preprotein moves through the TIM because of the membrane potential
differences across the IMM
c) It then associates with the mt-Hsp70 which also helps pull in through into the