Lecture 1

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Cell Biolgy ١

Lecture 1

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Cell Biolgy ٢

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Cell Biolgy ٣

Cell theory and the cell Cell theory and the cell

„ All animals consist of certain structural units

„ A term cell was used by Robert Hook in1965 Cork Cells were thought to have been these cells.

„ Cells are the fundamental units of life.

„ Anton von Leeuwenhoek was first to observe one

celled living things. Examples of these were bacteria and paramecium.

„ The concept that the cell is the basic unit of life is

known as the cell theory, which put by Schlieden an

Schwann

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Cell Biolgy ٤

Cell are divided into two main classes:

Cell are divided into two main classes:

„ Prokaryotic cells: lacks a nuclear envelope, smaller and simpler than eukaryotic cells, absence of nucleus, their genomes are less complex, they do not contain cytoplasmic

organelles or cytoskeleton.

„ Eukaryotic cells: have a nucleus in which the genetic material is separated from the

cytoplasm.

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Cell Biolgy ٥

Chapter I:

Chapter I:

Biological chemistry of the cell

Biological chemistry of the cell

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Cell Biolgy ٦

Chapter I: Biological chemistry of the cell Chapter I: Biological chemistry of the cell

This chapter focus on five major topics:

1- types of molecules within the cells

2- the structure and function of each type Molecular constituents of cells

Cells are composed of :

1- Macromolecules Organic molecules (carbon containing molecules like: lipids, proteins, nucleic acid,

carbohydrates)

2- Inorganic ions (water, salts, acids and bases)

3- Organelles (mitochondria, Golgi apparatus, nucleus)

4- Traces of Vitamins and minerals

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Cell Biolgy ٧

These constituents differ according to Cell type & Cell function

Molecular constituents of cells

.

(Biological Molecules)

(Water)

(Nucleic acids)

(Proteins) (Lipids) (Bases)

(Carbohydrate s)

(Organic)

(Inorganic ) (Acids)

(Salts)

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Cell Biolgy ٨

1 1 - - water water

Water is the most abundant compound found in living organisms (about 80%).

Properties of Water

„ Water as a Biological Solvent

- Cellular molecules bathed in water

- Water is an excellent solvent (a fluid in which something can be dissolved) for

many substances because of its polar nature.

- Polar substances and ions dissolve in water because opposite charges are

attracted. Ions are attracted to the appropriate ends of water molecules which

keep the ions dispersed in the water - or - dissolved.

„ Why Is water Polarity Important?

‰ Many macromolecules are also polar and readily dissolve in water

‰ Promotes the stability of large molecules through hydrogen bonding

‰ Forces non polar substances to aggregate

‰ Makes water cohesive

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Cell Biolgy ٩

1 1 - - water water

1- Strictly hydrophobic molecules, including most lipids, do not mix well with water

2- Some molecules have both hydrophobic and hydrophilic ends.

Such molecules are said to be amphipathic.

3- Amphipathic molecules make good emulsifiers because they can attract both hydrophobic substances and hydrophilic substances to them.

Water in Biochemical Reactions

• The breakdown and assimilation of many molecules of living organisms involves water. Water is needed to breakdown carbohydrates, lipids and proteins during digestion. The

formation of large biological molecules from smaller building

blocks releases water

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Cell Biolgy ١٠

There are four classes of biological molecules

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1- Carbohydrates

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2- Proteins

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3- Lipids

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4- Nucleic acids

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The four classes of biological molecules contain very large molecules

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They are often called macromolecules because of their large size

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They are also called polymers because they are made from identical building blocks strung together

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The building blocks are called monomers

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A cell makes a large number of polymers from a small group of monomers

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Proteins are made from only 20 different amino acids, and DNA is built from

just four kinds of nucleotides

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Cell Biolgy ١١

The monomers used to make polymers are universal

„

Monomers are linked

together to form polymers through dehydration

reactions, which remove water

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Polymers are broken

apart by hydrolysis, the addition of water

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All biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells

Unlinked monomer Short polymer

Longer polymer Dehydration

reaction

Hydrolysis

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Cell Biolgy ١٢

LIPIDS

LIPIDS

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Cell Biolgy ١٣

Lipids are water insoluble (hydrophobic, or water fearing) compounds

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They are soluble in organic solvents like chloroform, ether and benzene

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They are important in energy storage, They contain twice as much energy as a polysaccharide

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They are Amphipathic (possess hydrophilic and hydrophobic characteristics) macromolecules

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lipids have 4 major roles in cells

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The major component of cell membranes

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Play an important roles in cell signaling both as steroid hormones and as messenger molecules that convey signals from cell

surface receptors to targets within the cell

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Provide an important form of energy storage

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They are carriers of fat-soluble vitamins (A, D, E and K)

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Cell Biolgy ١٤

Lipids

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Simple lipids (fats, triglycerides): three fatty acids bonded to the C

₃

alcohol glycerol

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Complex lipids: simple lipids that contain additional

elements such as phosphorus, nitrogen, sulfur, or small

hydrophilic organic compounds (e.g., sugars)

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Cell Biolgy ١٥

Lipid categories

„ Lipids may be divided into the following categories:

„ fatty acyls

„ Glycerophospholipids

„ sphingolipids

„ Neutral fats

„ Plasmalogens

„ Steroids

„ Waxes

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Cell Biolgy ١٦

1- Fatty acids

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Fatty acids are major constituents of biological lipids

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The simplest lipids

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fatty acid are formed of two parts:

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- The hydrophilic head (COOH) which found in contact with the water of the environment and the internal part of the cell

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- The hydrophobic tail (long

Hydrocarbon chain, most frequently containing 16 - 18 carbon atoms) which is unable to interact with water

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This hydrophobic nature is

responsible for the formation of

biological membranes

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Cell Biolgy ١٧

Types of Fatty acids

„ Saturated fatty acids

„ Fatty acids with the maximum number of hydrogens are called saturated fatty acids

„ Most animal fat is saturated fat. Saturated fats, such as butter and lard, will pack tightly together and will be solid at room temperature

„ - Unsaturated fatty acids

„ Fatty acids contain one or more double bonds between carbon atoms called unsaturated fats because they have fewer than the maximum number of hydrogens.

„ This causes kinks or bends in the carbon chain because the maximum number of hydrogen atoms cannot bond to the carbons at the double bond

„ Plant and fish fats are usually unsaturated fats.

They are usually liquid at room temperature.

Olive oil and cod liver oil are examples.

„ The balance between saturated and unsaturated fatty acids is important in maintaining the

optimum degree of fluidity of a given membrane.

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Cell Biolgy ١٨

an ionic polar The salts of fatty acids have

long and a

carboxylate head group, the

polar hydrocarbon chain.

-

non

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Cell Biolgy ١٩

2- Neutral fats

- Fats are lipids made from one molecule of glycerol and three molecules of fatty acids

- Fatty acids link to glycerol by a dehydration reaction - They are mostly energy-storage molecules

- Fats are often called triglycerides because of their structure

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Cell Biolgy ٢٠

3- Phospholipids (Glycerophosphatides

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complex lipids containing phosphate groups;

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play a major structural role in cytoplasmic membranes

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structurally similar to fats but the third carbon atom of glycerol is bound to a phosphate group, which in turn attached to

another small polar molecules such as choline, serine