Basic biology for nurses

Biochemistry for nurses

Basic Biology for nurses: The Cell

Dr Hakim Mehenni

Email: [email protected]

https://sites.google.com/site/drhakimmehenni/


mailto:[email protected]

https://sites.google.com/site/drhakimmehenni/

General informations on the cellThe cell is a basic unit of living organisms.

It can perform all the functions of the organism: metabolism, movement, growth and reproduction.

There are 2 types of cells:

• Eukaryotic cell: It has a nucleus containing the genetic materials (ex: Human cells).

• Prokaryotic cell: It doesn’t have a nucleus and the genetic material is free inside the cell (ex: bacteria).


General view of the eukaryotic cell


The cell membrane

The cell is surrounded by a cell membrane (or plasma membrane)

The cell membrane is composed by:• A bilayers of phospholipides• Proteins (transmembrane,peripheral and intrinsic)• Cholesterols

The cell membrane is composed by:• A bilayers of phospholipides• Proteins (transmembrane,peripheral and intrinsic)• Cholesterols


The phospholipid bilayers Oil in water

Hydrophilic = Like water

Hydrophobic = Dislike water


• To protect the cell

• To control the exchanges between the cell and the outside environment (ex: Entrance of nutrients, disposal of wastes)

• To communicate with the outside environment (ex: others cells) through protein receptors present in the cell membrane.

Functions of the cell membrane


The membrane transports

The cell is alive! It needs the membrane transports in order to introduce nutrients (O2, glucose, etc…) from outside to inside the cell, and to reject

wastes (CO2, urea, etc…) from inside the cell to outside

Different types of membrane transports:

1. Passive transport:- simple diffusion- facilitated diffusion- osmosis (simple diffusion of water)

2. Active transport:- Uniporter pump- Symporter (co-transporter) pump- Antiporter pump

3. Endocytosis and exocytosis

Passive= No need of energy!

Active= Need of energy!


Passive transports No need of energy to work!

Simple diffusion

The simple diffusion is the movement of hydrophobic molecules (ex: O2, CO2, N2) from an area where they are more concentrated towards an area where they are less concentrated (concentration gradient) directly through the phospholipids bilayers membrane.


Facilitated diffusion

The facilitated diffusion is the movement of hydrophilic molecules (Na+, K+, glucose,etc…) from an area where they are more concentrated towards an area where they are less concentrated (concentration gradient) through transmembrane proteins (protein channels and carrier proteins).



Protein Channels for Na+ and K+ diffusion



Carrier Protein for

glucose diffusion


OSMOSIS

The osmosis is the simple diffusion of water (H2O) directly through the cell membrane from the area containing less solutes towards the area containing more solutes until equilibrating of the concentrations. Osmosis causes the electrolytes balance (Na+, Cl-, Ca2+, K+, etc…) on either side of the cell membrane.


Osmosis effect on red blood cells


Active transports Need energy to work!

The active transports need energy to work because:

• Movement against or in absence of a concentration gradient.• For hydrophilic molecules (ex: amino acids, glucose, Na+, K+, etc…) which are not able to cross directly through the bilayers phospholipids membrane.

The active transports use 3 types of transmembrane proteins:


ATP

ADP+Pi

Energy

HydrolysePhosphorylation

Hydrolyse of ATP provides a big energy (35 KJ). Each day, you hydrolyse 1025

ATP molecules in your body

ATP (Adenosine Triphosphate) is a molecule composed by an organic base (adenine) and a 3 phosphates group attached to a sugar (ribose).

ATP molecule is the source of ENERGY!


ATP molecule is the source of

ENERGY!

CELL METABOLISM (cell respiration)

ATP is manufactured inside the mitochondria from the transformation

of the energy coming from the absorbed foods into a chemical

energy stored in the chemical bond with the 3rd phosphate group.


Na+/K+/ATPase Pump (Antiporter)

The Na+/K+/ATPase Pump is present in the cell membrane.

The Na+ and K+ ions play many important roles in our body! For example they maintain the electrochemical potential of electrically excitable cells (ex: neurone or nerve cell).


Ca2+/ATPase Pump (uniporter)

The Ca2+/ATPase Pump is present in the endoplasmic reticulum membraneand the cell membrane.

The Ca2+ ions play an important role as second messenger in neurotransmitter release from neurons and in contraction of all muscle cell types.


Sucrose co-transporter pump (symporter)


Endocytosis and exocytosis transports

Endocytosis occurs by invagination of the cell membrane to form vacuoles(Cells of the immune defense). Exocytosis releases intracellular molecules to outside the cell. The molecules are transported in vacuoles (ex: Insulin released by the pancreatic cells (release of hormones))


The cytoplasm

The cytoplasm is the entire cellular material delimited by the cell membrane.It is composed by:

1. The cytosol liquid (85% of water, pH = 7):The cytosol contains simple molecules, macromolecules, dissolved gases (O2, CO2), ions (Na+, K+, Ca2+…)

2. The cell organites.There are 2 types of organites: Surrounded and non surrounded by a membrane


Organites non surrounded by a membrane


The cytoskeleton

The cytoskeleton is a dynamic protein structure: It is a skeleton and a musculature in same time for the cells. The cytoskeleton has the function to maintain the shape of the cell, to create a cell movement. It is involved in the cell division.


The ribosomes are spherical proteins which have the function to synthesis the proteins in the cell. They convert the instructions found in messenger RNA ( mRNA, which itself is made from instructions in DNA) into chains of amino-acids that make up proteins.


The centrosome is made by 2 centrioles which are protein tubules. The centriole is composed by 9 triplets of 3 protein tubules. Its function is to manage the movement direction during the cell division.


Organites surrounded by a membrane


The endoplasmic reticulum (ER) are organites with networks of intracellular membranes. The ER functions are to act as a manufacturing and packaging system. They are 2 types of endoplasmic reticulum:

• Rough endoplasmic reticulum (RER) who has its surface covered by ribosomes which assemble the amino-acids into proteins. The RER is connected with the membrane nucleus. RER is a packaging system of proteins.

• Smooth endoplasmic reticulum (SER) who doesn’t have ribosomes on its surface. The SER is involved in the synthesis and packaging of lipids, in the storing of calcium (Ca2+) and in the detoxification of the cell.


The Golgi Apparatus is composed of bags flattened on the others. He has the function to store the synthesized proteins coming from the rough endoplasmic reticulum. Then the proteins are concentrated inside vesicles in order to be secreted outside the cell by exocytosis. In summary the golgi apparatus plays a role of storing and secretion of the proteins.


The Lysosomes are vesicles containing digestive proteins (digestive enzymes) coming from the golgi apparatus. The lysosomes are the location of the cell digestion in which damaged organites, macromolecules and toxic molecules are destroyed.


The mitochondria is an organite having a double intracellular membrane. The mitochondria is the location of the ATP synthesis (ATP = source of ENERGY!) in presence of glucose and oxygen (O2) by a processus called « Cell Respiration ». The muscular cells have a large number of mitochondria.


Inside the mitochondria!


Phosphorylation

Hydrolyse

The nucleus is limited by a nuclear envelope containing:• The chromatin which is composed of DNA (DeoxyriboNucleic Acid = genetic support of the cell).• The nucleolus is the location of the DNA transcription (= synthesis of mRNA)•The nucleoplasm is the liquid inside the nucleus.

The nucleus is the brain of the cell!


The diameter of the nucleus is between 10 to 20 um.The nucleus has 2 main functions:

1. To control the biochemical reactions of the cell.

2. To save the genetic informations required for the life of the cell and its reproduction


Basic biology for nurses

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