Lecture 1 Cell Biology Overview. Tools of biochemistry to study the cell. Comparison of prokaryotic cell and Eukaryotic cell structure. Prepared by Mayssa Ghannoum

Cell: the fundamental unit of life The cell is as fundamental to the living systems of biology as the atom is to chemistry: all organisms are made of cells. In biological organization, the cell is the simplest collection of matter that can live. There are diverse forms of life existing as single-celled organisms. More complex organisms, including plants and animals, are multicellular. Cells are arranged into higher levels of organization, such as tissues and organs, but still they are an organism’s basic units of structure and function.

Study of cells: Microscopes and other tools of biochemistry It can be difficult to understand how a cell, usually too small to be seen by the unaided eye, can be so complex. There are two methods to study the cell: Microscopy Cell fractionation

Microscopy The discovery and early study of cells progressed with the invention of microscopes which are still indispensable for the study of cells. The major two types of microscopes are: 1. light microscope (LM) 2. electron microscope (EM) Two important parameters in microscopy are: Magnification: it’s the ratio of an object’s image size to its real size. Resolution: it’s a measure of the clarity of the image.

The size range of cells

LM vs EM Electron microscopes reveal many organelles and other subcellular structures that are impossible to resolve with the light microscope. But the light microscope offers advantages, especially in studying living cells. A disadvantage of electron microscopy is that methods used to prepare the specimen kill the cells.

II. Cell fractionation It’s a useful technique for studying cell structure and function, which takes cells apart and separates the major organelles and other subcellular structures from one another. The instrument used is the centrifuge, which spins test tubes holding mixtures of disrupted cells at various speeds. The resulting forces cause a fraction of the cell components to settle to the bottom of the tube, forming a pellet. At lower speeds, the pellet consists of larger components, and higher speeds produce a pellet with smaller components.

Properties of life Living organisms: are composed of cells are complex and ordered respond to their environment can grow and reproduce obtain and use energy maintain internal balance allow for evolutionary adaptation

Levels of Organization Cellular Organization :Each level of organization builds on the level below it but often demonstrates new features. 4.cells 3. organelles 2.molecules 1. atoms The cell is the basic unit of life.

Levels of Organization Organismal level Organism Organs systems Organs Tissues

Unifying themes in Biology Cell theory - All living organisms are made of cells, and all living cells come from preexisting cells. Molecular basis of inheritance - DNA encodes genes which control living organisms and are passed from one generation to the next.

Comparing Prokaryotic and Eukaryotic cells The basic structural and functional unit of every organism is one of two types of cells: Prokaryotic OR Eukaryotic . Only organisms of the domain Bacteria and Archaea consist of prokaryotic cells. Plants, animals, protists and fungi all consist of eukaryotic cells.

Comparing Prokaryotic and Eukaryotic cells All cells have several basic features in common: * They are all bounded by a selective barrier: The plasma membrane (will be discussed in details in lecture 3) * Enclosed by the membrane is a semifluid, jellylike substance: cytosol * All cells contain chromosomes, which carry gene in form of DNA. * All cells have ribosomes.

Comparing Prokaryotic and Eukaryotic cells Differences between prokaryotic and eukaryotic cells 1. The location of their DNA * In eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane. * In prokaryotic cell, there is no true nucleus. the DNA is concentrated in a region that is not a membrane-enclosed, called the nucleoid. 2. Membrane-bounded structures * Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of membrane-bounded organelles of specialized structure and function. * These membrane-bounded structures are absent in prokaryotic cells.

3. Size * Eukaryotic cells are generally much larger than prokaryotic cells. * Typical prokaryotic cell (bacteria) are 1-5 Micrometer in diameter. * Eukaryotic cells are typically 10-100 Micrometer in diameter. * Larger organisms do not generally have larger cells than smaller organisms—simply more cells.

Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

Nutrition of Prokaryotes Nutrition refers to how an organism obtains energy and a carbon source from the environment to build the organic molecules of its cells. Prokaryotes are grouped into four categories according to how they obtain energy and carbon

Nutrition of Prokaryotes Phototrophs: Organisms that obtain energy from light. Chemotrophs: Organisms that obtain energy from chemicals in their environment. Autotrophs: Organisms that use CO2 as a carbon source. Heterotrophs: Organisms that use organic nutrients as a carbon source.

Nutrition of Prokaryotes There are four major modes of nutrition Photoautotrophs: use light energy as energy source and CO2 as carbon source to synthesis organic compounds. Chemoautotrophs: use chemical inorganic substances as energy source, and CO2 as carbon source. Photoheterotrophs: use light as energy source and organic substances as carbon source. Chemoheterotrophs: use organic substances as a source for both energy and carbon.

Prokaryotic modes of nutrition Based on Carbon source and Energy source that can be used by a prokaryotic organism to synthesis organic compounds. Prokaryotes Autotrophs Heterotrophs CO2 as Carbon Source Organic compounds as Carbon Source Photo-autotroph Chemo-autotroph Photo-Heterotroph Chemo-Heterotroph - Light as energy source -CO2 as C source - Chemicals as energy source -CO2 as C source - Light as energy source -Organic compounds as C source - Chemicals as energy source - Organic compounds as C source

A panoramic view of the Eukaryotic cell The two basic types of eukaryotic cells are : Animal cell and Plant cell There are so many common structures between animal and plant cell, therefore there are major differences between them.

Animal cell

Plant cell

In plant cells but not in animal cells are found the following organelles: Chloroplasts: Photosynthetic organelle; converts energy of sunlight to chemical energy stored in sugar molecules. Cell wall: outer layer that maintains cell’s shape and protects it from mechanical damage; made of cellulose, and protein. Central vacuole: prominent organelle in plant cells. Function in storage, breakdown of waste products, hydrolysis of macromolecules; enlargement vacuole is a major mechanism of plant growth. Plasmodesmata: channels through cell walls that connect the cytoplasm of adjacent cells.