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Lecture 1

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Cell theory and the cellCell theory and the cell

All animals consist of certain structural unitsA 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 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 cytoplasmicorganelles or cytoskeleton.Eukaryotic cells: have a nucleus in which the genetic material is separated from the cytoplasm.

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Chapter I:Chapter I:

Biological chemistry of the cellBiological chemistry of the cell

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

This chapter focus on five major topics:1- types of molecules within the cells2- the structure and function of each type

Molecular constituents of cellsCells 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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These constituents differ according to Cell type & Cell function

Molecular constituents of cells.

(Biological Molecules)

(Water)

(Nucleic acids)

(Proteins) (Lipids)

(Bases)

(Carbohydrates)

(Organic)

(Inorganic)

(Acids)

(Salts)

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11-- waterwater

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

Properties of WaterWater as a Biological Solvent

- Cellular molecules bathed in water - Water is an excellent solvent (a fluid in which something can be dissolved) formany substances because of its polar nature.

- Polar substances and ions dissolve in water because opposite charges areattracted. Ions are attracted to the appropriate ends of water molecules whichkeep the ions dispersed in the water - or -

dissolved.Why Is water Polarity Important?

Many macromolecules are also polar and readily dissolve in waterPromotes the stability of large molecules through hydrogen bondingForces non polar substances to aggregateMakes water cohesive

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11-- waterwater

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 buildingblocks releases water

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There are four classes of biological molecules

1- Carbohydrates2- Proteins3- Lipids4- Nucleic acids

The four classes of biological molecules contain very large moleculesThey are often called macromolecules because of their large sizeThey are also called polymers because they are made from identical building blocks strung togetherThe building blocks are called monomers

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

Proteins are made from only 20 different amino acids, and DNA is built from just four kinds of nucleotides

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The monomers used to make polymers are universal

Monomers are linked together to form polymers through dehydration reactions, which remove waterPolymers are broken apart by hydrolysis, the addition of waterAll biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells

Unlinkedmonomer

Short polymer

Longer polymer

Dehydrationreaction

Hydrolysis

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LIPIDSLIPIDS

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

They are soluble in organic solvents like chloroform, ether and benzeneThey are important in energy storage, They contain twice as

much energy as a polysaccharideThey are Amphipathic (possess hydrophilic and hydrophobic characteristics) macromolecules

lipids have 4 major roles in cells The major component of cell membranes 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 cellProvide an important form of energy storage They are carriers of fat-soluble vitamins (A, D, E and K)

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Lipids

Simple lipids (fats, triglycerides): three fatty acids bonded to the C3 alcohol glycerolComplex lipids: simple lipids that contain additional elements such as phosphorus, nitrogen, sulfur, or small hydrophilic organic compounds (e.g., sugars)

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Lipid categories

Lipids may be divided into the following categories: fatty acylsGlycerophospholipidssphingolipidsNeutral fats PlasmalogensSteroidsWaxes

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1- Fatty acids

Fatty acids are major constituents of biological lipidsThe simplest lipidsfatty acid are formed of two parts:- The hydrophilic head (COOH)

which found in contact with the water of the environment and the internal part of the cell

- The hydrophobic tail (long Hydrocarbon chain, most frequently containing 16 - 18 carbon atoms) which is unable to interact with water This hydrophobic nature is responsible for the formation of biological membranes

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Types of Fatty acids

Saturated fatty acids Fatty acids with the maximum number of hydrogens are called saturated fatty acidsMost 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 bondPlant 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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an ionic polar The salts of fatty acids have long and a carboxylatehead group, the

polar hydrocarbon chain.-non

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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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3- Phospholipids (Glycerophosphatides

complex lipids containing phosphate groups;play a major structural role in cytoplasmic membranesstructurally 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