MEDICAL BIOLOGY

Lecture 1

Prof. MUDr. Roman Janisch, DrSc.Department of Biologyrjanisch@med.muni.cz

Structural Biology*

Cell Structure and Functions of Prokaryotic and Eukaryotic Cell

Introduction into Medical Biology

Why biology in medical studies? Characteristics of life Structural hierarchy of living systems Central position of the cell in biology Cell theory Cell structure Basic principles of functional structures of the cell Prokaryotic and eukaryotic cells Animal and plant cells Differentiation of a cell

Why biology in the medical studies? Medicine is a science dealing with the human body in health and

disease.

The human body is a living system and biology is concerned with general laws and principles governing living systems.

Knowledge of the common characteristics of living systems will facilitate understanding of the very complex human organism with all special aspects and processes of human physiology.

A good physician must know all about the human body and its functions and can achieve this only if they have good knowledge of basic natural laws.

Characteristics of lifeDifferences between living and inanimate nature

Chemical composition Cellular nature Metabolism Growth Reproduction Heredity Variation

Movement Evolution Irritability Differentiation Regeneration Adaptation

All these characteristics are required for the definition of a living system.The basic characteristic is chemical composition, all living systems a built up from organic biopolymers.

Structural hierarchy of living systems

1. Subcellular organisms (acellular) - viruses, phages.

2. Unicellular organisms - bacteria, cyanobacteria, protozoa (Paramecium, Amoeba), algae (Chlamydomonas), fungi (yeast cells).

3. Cell colonies - algae (Volvox), slime mould (Physarum).

4. Multicellular organisms - animals, plants, fungi.

5. Animal societies - social insects (honeybee society, termites, etc.)

Building hierarchy in multicellular organisms1. Atoms (carbon, oxygen, hydrogen, nitrogen)

2. Molecules (actin, tubulin, globulins, DNA, RNA)

3. Supramolecular complexes (microtubules, membranes)

4. Organelles (mitochondria, chloroplasts, lysozomes)

5. Cells (neurones, muscle cells, leukocytes)

6. Tissues (connective, epithelial, muscle, nervous tissues)

7. Organs (stomach, salivary gland, brain, eye, heart)

8. Systems of organs (digestive, respiratory, excretory)

9. Organisms (human)

Cell theory Central position of the cell in biology. Mid-19th century Schleiden, Schwann, Purkinje. The cell is a basic structural and functional unit of all organisms. All forms of life are associated with cells. Except for viruses, all living systems are

based on cells. All cells have a uniform principle of structure. The size range is 0.3 μm - 3 mm. Cells are differentiated according to their structure and function. Examples of differentiated cells - yeast cell, infusorian, amoeba, alga, erythrocyte,

leukocyte, neurone, fibroblast, chondrocyte, epithelial cell, smooth muscle cell, gland cell, gamete, receptor cell.

Morphology of any differentiated cell depends on its function. Molecular biology confirmed cell theory principles by the discovery of universality

of the genetic code.

Cell Structure

The previous cytological view on the cell structure distinguished morphology from function of different cell components (organelles).

Recent technologies have revealed new details of microscopic, submicroscopic and molecular structures.

Findings in molecular biology eliminated the gap between morphology and function of cell structures.

In the current concept of cell biology structure and function together are understood in terms of three basic structural and functional principles of the cell.

Cell Structures in Different Cell Types

Basic structural and functional principles of a Basic structural and functional principles of a cellcell

Cell memory principle(nucleic acids, proteins,chromosomes, nucleosomes, ribosomes)

Membrane principle (biomembranes, plasma membrane,nuclear envelope, endoplasmic reticulum, vacuoles, Golgi apparatus, lysozomes, mitochondria, chloroplasts)

Cytoskeletal principle (microtubules, centrioles, kinetosomes, axonemes, microfilaments, intermediate filaments)

The cell is a complex hierarchical system.

Molecular and cell biology, previously cytology, is a field of science dealing with cells.

Cell Memory Memory is ability to record and store information.

Biological memory is based on storage of information in living systems and is therefore called genetic information.

Genetic information is a complex system carrying complete data necessary for the existence of one’s own life and reproduction.

Cell memory system has to be large, stabilised, permanent in time, fast in expression into traits, able to duplicate, change and develop.

DNA is the main information medium in all living systems.

Biomembranes

Cells need membranes to:

compartmentalize and delineate the cell and its organelles

regulate the flow of materials, energy and information

mediate recognition of environmental factors

mediate interaction between cells

Biomembranes

Historical Data on Membrane Structure Research

Presence of lipids (Overton 1890)

Monolayer of phospholipids (1905)

Bilayer of phospholipids (Gorter a Grendel 1925)

Bilayer of phospholipids and protein layers (Dawson a Danielli 1935)

Unite membrane (Roberton 1960)

Fluid mosaic model (Singer and Nicolson 1972)

Structure of membrane proteins (Unwin and Henderson (1972)

Molecular Structure of Biomembranes

The asymmetrical distribution of phospholipids and glycolipids in a plasma membrane lipid bilayer

Transmembrane proteins

Ways in which membrane proteins associate with the lipid bilayer

The cytoskeleton

A skin cell (fibroblast) in culture has been fixed and stained with Coomassie blue, a general stain for proteins.

Various filamentous structures extend throughout the cell.

The dark body in the center is the nucleus.

Basic Components of the Cytoskeleton

Microtubules

Microfilaments

Intermediary filaments

Three types of cytoskeletal components

Three types of cytoskeletal components

Functions of the Cytoskeleton

Maintenance of cell structure

Movement

Information medium

Prokaryotic and Eukaryotic Cells There are two categories of cells from the point of view of evolution and their structural arrangement - prokaryotic and eukaryotic cells.

Differences: cell size

membrane organelles

type of DNA

RNA and protein synthesis

ribosomes

cytoskeleton

cell division

Differences between prokaryotic and Differences between prokaryotic and eukaryotic cells:eukaryotic cells:

Cell strctures Prokaryotic cell Eukaryotic cell

Nuclear envelope none present

Chromosomes single, circular more then one, linear

Membranel organelles minimun multiple and diverse

Ribosomes small size large size

Cytoskeleton none present

Cell reproduction binary cell division mitosis

Cell wall present present only in plants and fungi

Structure of Prokaryotic and Eukaryotic Cell

Cell’s Evolution TreeThe three major domains of the living world

The tree is based on comparison of the nucleotide sequence of ribosomal RNA subunit in the difference species.The lengths of the lines represent the number of evolutionary changes that have occurred in this molecule in each lineage. Bacteria recently has been redefined to refer to eubacteria specifically.

Animal and Plant Cells

Differences in structure

There are three cell structures typical of plant cells:

cell wall

plastids

vacuole

Animal Cell

Plant Cell

Differentiation of the Cell

Differentiation during phylogenesis and ontogenesis.

Specialisation in function.

Regulation of differentiation - regulation of gene expression.

Failure of regulation – congenital defects, cancerogenesis.

GlossaryAlga A photosynthetic, plant-like protist.

Archaea The domain name for achaebacteria.

Basal body

A cylindrical structure at the base of a cilium or a flagellum consisting of nine sets of triplet microtubules from which the microtubules forming axonemes radiate; a synonym for kinetosome; a homologous structure for centriole.

Binary fission A type of cell division in prokaryotes; each dividing daughter cell receives a copy of the single parental chromosome.

Biological memory Biological memory is based on ability to record and store information in living systems; it is also called genetic information.

Cell theory Schleiden, Schwann, and Purkinje recognized in the 1850s that the cell is a basic structural and functional unit of all organisms, that all forms of life are associated with cells, and that the structure of a cell is organised by a uniform principle.

Cellular differentiation Structural and functional divergence of cells as they become specialized during the development of a multicellular organism; dependent on control by gene expression.

Centriole An organelle having the same structure as a kinetosome (basal body); part of the microtubule-organising centre (MTOC).

Centrosome A structure in the cytoplasm of eukaryotic cells, consisting of two centrioles and pericentriolar matrix, important during cell division; also called microtubule-organising centre (MTOC).

Chloroplast An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

Chromatin Aggregate mass of dispersed genetic material composed of DNA and protein, and observed between periods of cell division in eukaryotic cells.

Cilium A membrane-enclosed locomotory structure extending from the surface of eukaryotic cells and composed of nine peripheral and one central doublets of microtubules called axonemes. Numbers of them cover the whole cell surface. See also flagellum.

Coated vesicles Transport vesicles surrounded by an outer protein cage composed primarily of the fibrous protein clathrin.

Cyanobacteria Photosynthetic, oxygen-producing bacteria (formerly known as blue-green algae).

Cytology A science dealing with cell structure and function.

Cytoskeleton A network of protein fibrils resistant to non-ionic detergent , i.e., microtubules, microfilaments and intermediate filaments that serve a variety of mechanical, motor and transport functions.

Cytosol The semifluid portion of cytoplasm.

Early endosomes Organelles that arise from clathrin-coated vesicles that have lost their coat after endocytosis.

Eukaryotic cell A cell with a membrane-enclosed nucleus and membrane-enclosed organelles, comprising protists, plants, fungi, and animals (eukaryotes).

Eukaryotic chromosome A structural unit of the genetic material consisting of a single, linear double-stranded DNA molecule and associated proteins, particularly histones aggregated into nucleosomes.

Extracellular matrix A usually insoluble network consisting of glycosaminoglycans, collagen, and various adhesive proteins secreted by animal cells.

Flagellum A membrane-enclosed locomotory structure extending from the surface of eukaryotic cells and composed of nine peripheral and one central doublets of microtubules, called axonemes. One or several of them are attached to the cell pole. See also cilium.

Fluid mosaic model The model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

Gene expressibility The process by which information encoded in a gene is converted into an observable phenotype (most commonly the production of protein).

Golgi apparatus An organelle in eukaryotic cells, consisting of stacks of membranes that modify, store, and route products of the endoplasmic reticulum.

Intermediate filament A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments (mostly 10 – 16 nm)

Kinetosome A synonym for basal body and a homologous structure for centriole.

Lysosome A membrane-enclosed bag of hydrolytic enzymes present in the cytoplasm of eukaryotic cells.

Microfilament A solid rod of actin protein in the cytoplasm of eukaryotic cells, part of the cytoskeleton acting with myosin to cause cell contraction.

Microtubule A hollow rod of tubulin protein in the cytoplasm, flagella and cilia of eukaryotic cells.

Microvillus One of many fine, finger-like projections of animal cells which increase their surface area.

Mitochondrion A membrane organelle in eukaryotic cells that serves as the site of cellular respiration.

Nuclear envelope The membrane that encloses the nucleus, separating chromosomes from the cytoplasm, in eukaryotic cells.

Nuclear lamins A group of intermediate filament proteins that form a fibrous network on the inner surface of the nuclear envelope.

Nuclear pore A protein-lined channel through the nuclear envelope that permits passage of RNA from the nucleus to the cytoplasm and transport of proteins in the opposite way.

Nucleolus A specialized structure in the nucleus formed by parts of various chromosomes that is active in the synthesis of ribosomes.

Nucleosome A basic bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histones.

Nucleus The chromosome-containing organelle of a eukaryotic cell.

Organelle One of several structures with specialised functions, suspended in the cytoplasm of eukaryotic cells.

Peroxisome A vesicle-like organelle containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.

Phage A virus that infects bacteria; also called bacteriophage.

Phospholipids Molecules that constitute the inner bilayer of biomembranes; they have a polar, hydrophilic end, and a non-polar, hydrophobic tail.

Plasma membrane A membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the flow of molecules, energy and information.

Plasmodesma Any of many minute strands of cytoplasm that extend through plant cell walls and connect adjoining cells

Plastids Major organelles found only in plants and algae, responsible for photosynthesis and storage of products like starch.

Prokaryotic cell A cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles.

Prokaryotic chromosome One double stranded DNA molecule arranged in a circle.

Prokaryotic flagellum A synonym for bacterial flagellum; its width is one tenth of that of an eukaryotic flagellum; it is not covered by a membrane and is composed of flagellin.

Ribosome A cell organelle arising in the nucleolus, consisting of two subunits and functioning as the site of protein synthesis in the cytoplasm.

Rough endoplasmic reticulum The portion of endoplasmic reticulum studded with ribosomes.

Smooth endoplasmic reticulum The portion of endoplasmic reticulum free from ribosomes.

Tissue An integrated group of cells with a common structure and function.

Tonoplast A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.

Vacuole A membrane enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development.

Yeast A unicellular fungus primarily reproducing asexually by simple cell division or by budding of a parent cell.