Basic information on cell cell membrane and its

Basic information on cell: cell membrane and its function, organelles, general types of tissues of human origin CEAC 514 Assoc. Prof. Dr. Yasemin G. İşgör

Typical Animal Cell

MEMBRANE STRUCTURE Similar to any container, the first noticeable thing is the presence of boundaries around the cells or in biological terminology; MEMBRANES. Biological membranes consist of phospholipid bilayers with various sorts of PROTEINS interspersed in them and located on the membrane surfaces according to the widely accepted FLUID MOSAIC MODEL of membrane structure Fluid mosaic model of biological membranes

MOVEMENT OF MATERIALS ACROSS MEMBRANES All materials (including the cellular solvent: H 2 O) move across membranes through highly regulated mechanisms. A membrane is said to be “permeable” to a substance if it allows free passage of that substance. It is often stated that cellular membranes are SEMIPERMEABLE, meaning solvents but not solutes may cross. The living cell membranes “is not openly permeable” to any substance, including, H 2 O, although H 2 O may cross more freely than most other substances. Of these mechanisms, three shall be mentioned due to their importance in culturing of cells: 1. Osmosis: 2. Simple Diffusion 3. Active Transport

Hypotonic, hypertonic and isotonic Solutions When a solute is more concentrated on one side of a membrane than the other, a concentration gradient exists. If a solvent is capable of traversing a membrane it will move from the side where the solute is more dilute (hypotonic: free water is high), to the side of solute concentration is high (hypertonic: free water is less). Solvent molecules continue to move until the concentrations are equal across both sides of the membrane (isotonic).

1. Osmosis: The process by which a solvent crosses a membrane in response to a concentration gradient is known as OSMOSIS and the force with which the solvent is drawn from dilute solute side to the concentrated side is the OSMOTIC PRESSURE.

2. Simple Diffusion Many solutes are dissolved in the cellular solvent which is H 2 O Dissolved solute across membranes by moving from a higher concentration (of solute) side to the lower concentration side by the involvement of special membrane proteins. • This is called simple diffusion and actually it is moving down a concentration gradient from high to low solute concentrations. • The rate of diffusion through a membrane is known as flux.

3. Active Transport Unlike diffusion, active transport is able to achieve a net movement of a solute “UPHILL” against a concentration gradient. To accomplish this task the cell must use ATP as the energy source Nearly all cells (either prokaryotic or eukaryotic) use active transport to pull valuable molecules like sugars. in a resting human body, for example, 30 -40% of all energy used goes in to active transport and the percentage may be much higher in certain organs such as brain and kidneys.

PROKARYOTIC CELL STRUCTURE Ribosomes Flagella Cytoplasm Chromosome Cell wall Cell membrane

EUKARYOTIC CELL STRUCTURE Eukaryotic cells are characterized by internal membrane systems and by compartmentalization that subdivides the chemical activities. These membrane bound structures within eukaryotic cells are called ORGANELLES

EUKARYOTIC CELL STRUCTURE: NUCLEUS-1 . The cell’s nucleus is surrounded by the NUCLEAR ENVELOPE which consists of two layers of membranes with a narrow space between them. Macromolecules (m. RNA, r. RNA, nuclear proteins etc) can exit or enter the nucleus through PORES, which provide communication routes for with the surrounding cytoplasm.

EUKARYOTIC CELL STRUCTURE: NUCLEUS-2 Within the nucleus, DNA is organized in linear arrays of NUCLEOSOMES.

EUKARYOTIC CELL STRUCTURE: ENDOPLASMIC RETICULUM-1 ER is a network of flattened tubes surrounding the nucleus is actually of two types: 1) rough endoplasmic reticulum (RER) and 2) smooth endoplasmic reticulum (SER).

EUKARYOTIC CELL STRUCTURE: ENDOPLASMIC RETICULUM-2 1) Rough Endoplasmic Reticulum (RER) surface is studded with ribosomes. This is the place where proteins are synthesized by translation of the m. RNA. 2) smooth endoplasmic reticulum (SER) do not contain ribosomes and do not function in protein synthesis. SER contains phospholipids, neutral fats, sterols and other lipids that it is the site for lipid biosynthesis.

EUKARYOTIC CELL STRUCTURE: GOLGI APPARATUS In most eukaryotic cells, one or more GOLGI BODIES (Apparatus) are present in the form of membranous sacs (transfer vesicles) Membranous sacs (transfer vesicles) from RER and SER bring proteins and lipids to the golgi body, where they are repackaged into secretory vesicles. These vesicles then move to the plasma membrane where their contents are expelled from the cell (Exocytosis) Golgi bodies also carry on synthesis. In them, proteins from the RER are converted to glycoproteins, polysaccharides of various sorts and mucoproteins which form the mucus are synthesized. • Golgi bodies also carry on synthesis. In them, proteins from the RER are converted to glycoproteins, polysaccharides of various sorts and mucoproteins which form synthesized. the mucus are

EUKARYOTIC CELL STRUCTURE: LYSOSOMES . membrane-bound organelles that contain a variety of powerful hydrolytic enzymes which catalyze the breakdown of large biological molecules The separation of hydrolytic enzymes from the cytoplasm by the lysosome’s membrane protects the normal working components of a living cell from random destruction (digesting itself). • Lysosomes vary in size and appearance, and probably derived either from the ER or Golgi bodies (or from both).

EUKARYOTIC CELL STRUCTURE: MITOCHONDRIA act as power plants in the energy system of eukaryotic cells. The output of this energy production is the high compound called ATP (Adenosine triphosphate) Mitochondria have double membrane system; the outer one is fairly typical, unspecialized unit membrane, but the inner one is highly specialized for ATP production. Elaborate folds of this inner membrane (CRISTA) extend into the mitochondria’s interior gel-like matrix (STROMA)

RECALLING THE BASIC TISSUE-CELL KNOWLEDGE-1 Over 200 Cell types in the human body are assembled to form variety of tissues such as: Epithelia, Connective tissue, Muscle, and Nervous tissue Most of these tissues contain mixtures of cell types (non-homogeneous). Epithelia is the sheets of cells that forms the inner and outer lining of the organs and surface of the body. Some has main function to increase absorption (absorptive cells), some have transport function to facilitate the transport of substances (such as mucus) over the epithelial sheet (ciliated cells) and some have function to secrete substances out of cell (secretory cells). Absorptive cells Ciliated cells Secretory cells

RECALLING THE BASIC TISSUE-CELL KNOWLEDGE-2 Connective tissue is in between the organs and tissues to create more interaction, provide strength, and as the name implies connects the solid structures (between bones). It is mainly composed of a strong fibrous protein network (collagen and elastin) in polysaccharide gel. This forms a structure called extracellular matrix secreted mainly by fibroblasts. Also bone cells (osteoclasts) secrete to extrtacellular matrix, and these secretion becomes a crytal of calcium phosphates and keep bone cells together in solid matrix structure. osteoclasts Osteoclasts in calcium phosphate deposited matrix.

OTHER TYPE OF CELLS THAT FORMS THE BODY STRUCTURE Nerve tissue: is made of nerve cells called neurons.

Muscle cells Blood cells