Define The cell organelles .

Describe the comparison between

prokaryotic and eukaryotic cells

Determine the types of cell.

List the types of organelles.

Describe the Mitochondrial Inheritance .

Nice to know the Mitochondrial diseases .

Nice to know the clinical features of the

Mitochondrial diseases in this lecture.

In cell biology: an organelle is a specialized subunit within a cell that has a specific function, and it is usually separately enclosed within its own lipid bilayer.

The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive).

Organelles are identified by microscopy, and can also be purified by cell fractionation.

There are many types of organelles, particularly in eukaryotic cells. While prokaryotes do not possess organelles.

The prokaryotic cell is a simple cell. It has no nucleus, and no membrane-bound organelles. The genetic material of a prokaryotic cell is found in a region of the cell known as the nucleoid. Bacteria are a fine example of prokaryotic cells and divide by a process known as binary fission; they duplicate their genetic material, divide in half, and produce two identical daughter cells.

The eukaryotic cell is much more complex. It contains a nucleus, which functions as the control center of the cell, directing DNA replication, transcription, and cell growth. Eukaryotic organisms may be unicellular or multicellular. One of the key features of eukaryotic cells is the presence of membrane-bound organelles, each with its own duties.

Prokaryotes Eukaryotes

Typical organisms bacteria, archaea protists, fungi,

plants, animals

Typical size ~ 1–5 µm[10] ~ 10–100 µm[10]

Type of nucleus nucleoid region; no

true nucleus

true nucleus with

double membrane

DNA circular (usually)

linear molecules

(chromosomes) with

histone proteins

Ribosomes 50S and 30S 60S and 40S

Cytoplasmic

structure very few structures

highly structured by

endomembranes and a

cytoskeleton

Cell

movement flagella made of flagellin

flagella and cilia

containing microtubules;

lamellipodia &filopodia

containing actin

Mitochondria none

one to several thousand

(though some lack

mitochondria)

Chloroplasts none in algae and plants

Organization usually single cells

single cells, colonies,

higher multicellular

organisms with

specialized cells

Cell division Binary fission (simple

division)

Mitosis (fission or

budding)

Meiosis

Prokaryotic Organelles:

Plasma membrane:

1- This is a selective barrier around a cell

composed of a double layer of phospholipids.

2- Part of this selectivity is due to the many

proteins that either rest on the exterior of

the membrane or are embedded in the

membrane of the cell.

3- Each membrane has a different

combination of lipids, proteins, and

carbohydrates that provide it with its unique

characteristics.

Cell wall: This is a wall or barrier

that functions to shape and protect

cells. This is present in all

prokaryotes.

Ribosomes: These function as the

host organelle for protein synthesis

in the cell. They are found in the

cytoplasm of cells and are composed

of a large unit and a small subunit.

Eukaryotic Organelles:

Ribosomes:

1) As in prokaryotes, eukaryotic.

2) ribosomes serve as the host organelle for

protein synthesis.

3) Eukaryotes have bound ribosomes, which are

attached to endoplasmic reticula and form

proteins that tend to be exported from the cell

or sent to the membrane.

4) There are also free ribosomes, which exist

freely in the cytoplasm and produce proteins

that remain in the cytoplasm of the cell.

5) Eukaryotic ribosomes are built in a structure

called the nucleolus.

Prokaryotic ribosomes Eukaryotic ribosomes

Smooth endoplasmic reticulum:

This is a membrane-bound organelle involved in lipid synthesis, detoxification, and carbohydrate metabolism.

Liver cells contain a lot of smooth endoplasmic reticulum (SER) because they host a lot of carbohydrate metabolism (glycolysis).

The liver contains much SER for another reason—it is the site of alcohol detoxification.

It is given the name "smooth" endoplasmic reticulum because there are no ribosomes on its cytoplasmic surface.

Rough endoplasmic reticulum: This membrane-bound organelle is termed "rough" because of the presence of ribosomes on the cytoplasmic surface of the cell. The proteins produced by this organelle are often secreted by the cell and carried by vesicles to the Golgi apparatus for further modification.

Golgi apparatus: Proteins, lipids, and other macromolecules are sent to the Golgi to be modified by the addition of sugars and other molecules to form glycoproteins. The products are then sent in vesicles to other parts of the cell, directed by the particular changes made by the Golgi, in other words: storage & packaging of materials that will be exported from the cell.

Rough endoplasmic reticulum Golgi apparatus

Nucleus: This is the control center of the

cell. In eukaryotic cells, this is the storage

site of genetic material (DNA).

It is the site of replication, transcription,

and posttranscriptional modification of RNA.

It also contains the nucleolus, the site of

ribosome synthesis.

Vacuole: This is a storage organelle that acts

as a vault.

Vacuoles are quite large in plant cells but

small in animal cells.

Nucleus Vacuole

Chloroplast: This is the site of photosynthesis and energy production in plant cells. Chloroplasts contain many pigments, which provide leaves with their color. Chloroplasts are divided into inner portion and outer portion. The inner fluid portion is called the stroma, which is surrounded by two outer membranes. Winding through the stroma is an inner membrane called the thylakoid membrane system, where the light-dependent reactions of photosynthesis occur. The light-independent (dark) reactions occur in the stroma.

Cytoskeleton:The skeleton of cells consists of three types of fibers that provide support, shape, and mobility to cells: microtubules, microfilaments, and intermediate filaments.

- Microtubules are constructed from tubulin and have a lead role in the separation of cells during cell division. Microtubules are also important components of cilia and flagella, which are structures that aid the movement of particles .

- Microfilaments, constructed from actin, play a big part in muscular contraction.

- Intermediate filaments are constructed from a class of proteins called keratins and are thought to function as reinforcement for the shape and position of organelles in the cell.

Chloroplast Cytoskeleton

Peroxisomes:

1-are single-membrane structures found in all eukaryotic cells. They are small, membrane-bound structures that use molecular oxygen to oxidize organic molecules.

2-These are organelles containing enzymes that produce hydrogen peroxide as a by-product while performing various functions, such as breakdown of fatty acids and detoxification of alcohol in the liver.

3-Peroxisomes also contain an enzyme that converts the toxic hydrogen peroxide by-product of these reactions into cell-friendly water.

are special types of vacuoles .

contain enzymes for use in the hydrolytic

breakdown of macromolecules .

Three ways to enter a lysosome –

phagocytosis , autophagy, and receptor-

mediated endocytosis.

Found in ALL eukaryotic cells (even in plant cells)

Site of aerobic respiration sugars + O2 - - > ATP + CO2 + H2O

So it called “powerhouse of the cell”

Contain DNA which codes for mitochondrial proteins, ribosomes, etc.

Divide by a process similar to binary fission when cell divides.

Enclosed in a double membrane system. Inner Membrane forms the Cristae (invaginations into

interior region) Site of energy generation

Matrix is the soluble portion of the mitochondria Site of carbon metabolism

Location of mDNA

Site of mitochondrial protein synthesis

Mammalian cells contain mitochondria which have their own circular deoxyribonucleic acid (mtDNA). Mitochondria are only passed on in the cytoplasm of the egg so that a child inherits all its mitochondria from its mother. There are some diseases that are some diseases that are associated with mutations in mitochondrial DNA. A woman with such a mutation will therefore pass it on to all her children whilst a man with the same mutation will not pass it on to any of his children.

There is often a wide range of severity of disease in carriers of mitochondrial mutations. Mitochondrial inheritance is characterized by:

1-Maternal transmission only.

2-Extreme variability in the same family.

The genetics of mtDNA differ from that of DNA in the following unique properties:

1-The mitochondrial genome is maternally inherited:

The mother transmits her oocyte mtDNA to all of her offspring & her daughters transmit their mtDNA to the next generation. This is due to the fact that during fertilization. The few mitochondria from the sperm that enter the egg are rapidly eliminated through unknown mechanism.

2-Mitochondria are polypoid:

Each human cell has hundreds of mitochondria each containing 2-10 mtDNA molecules. At cell division mitochondria and their genomes are randomly distributed to daughter cells.

3-The mitochondrial genome has a much faster evolution rate than the nuclear genome:

The average number of base pair difference between two human mitochondrial genomes is estimated to be from 9.5 to 66. This explained by the fact that, although the mitochondrial gamma-DNA polymerase may retain a proofreading activity X certain types of repair enzymes have been identified in mitochondrial fractions.

Mitochondria lack an efficient DNA repair system, based, for instance, on homologous recombination or removal of pyrimidine dimmers. In addition, the mitochondrial genome lacks protective proteins like histones, and is physically associated with the inner mitochondrial membrane, where highly mutagenic oxygen radicals are generated as by-products of OXPHOS.

Normally, the mitochondrial genotype of an

individual is composed of a single mtDNA

species:

A condition known as homoplasmy.

However, the intrinsic propensity of mtDNA

to mutate randomly can occasionally

determine a transitory condition known as

heteroplasmy, where the wild-type & the

mutant genomes co-exist intracellular.

Assorted myopathies and neuropathies observed clinically in recent years:

neurologic disorders

ragged red fibers in muscle biopsies

weakness exacerbated by exercise

seizures

(muscle jumps)

dementia with early onsetmovement disorders

stroke-like symptoms

retinopathy

hearing loss

partial blindness

migraine headaches

Combined oxidative

phosphorylation deficiency 5

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