Structure and Organization of Eukaryotic cell Plasma membrane

Structure and Organization of Eukaryotic cell

Plasma membrane • Eukaryotes resemble Prokaryotes in membrane structure and functions except for sterols • Source: http: //bioweb. wku. edu.

Cell wall • Cell wall is quite simple. • In algae and plant cells, the cell wall is usually composed of cellulose. • In molds it is composed of chitin and/or cellulose. • Animal cells and protozoans lack cell walls.

Flagella and Motility in eukaryotes • Many eukaryotic microorganisms move by flagella and cilia • Cilia are shorter than flagella - structurally similar • Flagella are long, flexible structures move in a whiplash fashion • Both consist of 9 fused pairs of protein microtubules (tubulin) with side arms of the motor molecule dynein that originate from a centriole. These form a ring around an inner central pair of microtubules that arise from a plate near the cell surface. The arrangement of microtubules is known as a 2 X 9+2 arrangement. This complex of microtubules is surrounded by a sheath continuous with the cytoplasmic membrane.

Source: http: //. micro. magnet. fsu. edu • cilia are more in numbers, beat in a coordinated fashion called metachronal rhythm • Amoeba and slime moulds show a movement produced by their cytoplasm, called cytoplasmic streaming • produces projections, called pseudopodia

Mitochondria • Approximately the same size as bacteria • Number - varies in cells • The process of respiration and oxidative phosphorylation localized in mitochondria • The mitochondrial membranes lack sterols. ATP synthesized within the mitochondrion can move into the cytoplasm • Cristae - project into the mitochondrial lumen

• enzymes involved in ATP production are located within the inner membrane • Enzymes of TCA cycle and β – oxidation are located in the matrix • Mitochondria use its DNA, ribosomes to produce some of its own proteins • Mitochondria reproduce by binary fission

Chloroplasts • All photosynthetic eukaryotic organisms, possess chloroplasts • structures of chloroplast reveals thylakoids • thylakoid membrane is impermeable to ions well suited for its role in protein translocation • thylakoids are stacked grana • stroma of chloroplasts contain enzymes for reduction of CO 2 to organic material • outer chloroplast membrane is highly permeable • Although some bacteria are photosynthetic, do not possess chloroplasts

Structure of a chloroplast

Eukaryotic ribosomes

Endoplasmic Reticulum and Golgi bodies • The endoplasmic reticulum or ER is a maze of parallel membranous tubules and flattened sacs surrounding the nucleus that connects with the nuclear membrane and runs throughout the cytoplasm • provide a surface area for protein and lipid synthesis; • form a pathway for transporting molecules within the cell; and • provide a storage area for molecules the cell has synthesized. • Golgi • sort proteins and lipids received from the ER; • modify certain proteins and glycoproteins; and • sort and package these molecules into vesicles for transport to other parts of the cell or secretion from the cell.

Nuclei • Eukaryotic organisms possess a nuclear envelope contains the genetic material • envelope consists of two membranes • outer membrane carries ribosomes and forms continuous structure with the endoplasmic reticulum and cytoplasmic membrane • nuclear envelope encloses chromosomes in chromosomal proteins • called histones • DNA exists as a single linear molecule to which histones and other proteins are attached • number of chromosomes vary from a few to many hundreds

Structure of a nucleus Source: http: //micro. magnet. fsu. edu. • Eukaryotic cells contain much more DNA than do bacteria, • DNA is organized as multiple chromosomes located within a nucleus. • The nucleus in eukaryotic cells is separated from the cytoplasm by a nuclear envelope • The nucleus divides my mitosis , a process that ensures each daughter cell receives the same number of chromosomes as the original parent cell. • Haploid sex cells are produced from diploid cells by meiosis

The cytoskeleton • cytoplasm of eukaryotic cells contain network of microfilaments and microtubules • filaments contain a number of proteins including actin and myosin • Cytoskeleton maintenance of cell shape, positioning cell organelles cell motility (Spirochactes is an exception among Prokaryotes in having cytoskeleton)

Cytoskeleton http: //academic. brooklyn. cuny. edu.

Comparison of Prokaryotic and Eukaryotic cell

Characters Prokaryotes Eukaryotes Groups where found Bacteria, Cyanobacteria, Archaea Algae, Fungi, Protoza, Plants and Animals Size 1 -2 by 1 -4 µm or less Greater than 5 µm Cell wall Made up of peptidoglycan Made of cellulose in algae and plants, of fungal cellulose or chitin in fungi, absent in protozoan and animals Osmotic control Wall possesses mechanical strength necessary to counter balance turgor pressure of cytoplasm Plasma membrane Does not contain sterols except in Mycoplasma Maintained by contractile vacuole Sterol present Plasma membrane is the Several cell organelles also covered only membrane by membrane (Unit membrane) Plasma membrane folded to form mesosomes. Mesosomes are absent, but in animal cells, it is folded to form finger like microvilli.

Cytoplasm Ribosomes Granular due to presence Fibrillar made up of fibrous of ribosomes, fibrous proteins which form fibrous cytoskeleton absent cytoskeleton 70 S, freely distributed in 80 S free as well bounded to ER. cytoplasm 70 S in mitochondria and chloroplast. Mitochondria Chloroplast Absent Present Absent, in cyanobacteria Present in plant cells and absent thylakoid vesicles present. in fungi, protozoa and animal cell. Golgi apparatus Absent Present Lysosomes Absent Present Endoplasmic Reticulum Absent Present Peroxisomes Absent Present Centrioles Absent Present

Nucleolus Absent Present True vacuoles Absent Present Gas vesicles Present Absent Made up of flagellin fibrils. Made up of tubulin Flagellin sub-units arranged microtubules arranged in in a ring helically around a 9+2 formation and carboxysomes Flagella central core. Pili Present Absent Cilia Absent Present in protozoans

Chromosome Usually 1 Variable, 2 to many number DNA Circular, single chromosome, Single, linear, double single or double stranded, helically coiled, usually haploid coiled, chromosome. Extranuclear DNA Present in bacteria (plasmid 0. 1 diploid. Absent except in -5% of bacterial chromosome) yeasts Histone proteins Absent Present DNA position, Usually central, not surrounded Surrounded by nuclear membrane

Locomotion Present in some Absent in plants, algae, fungi, except in bacteria, by flagella. zoospores and few unicellular algae and fungi, present in animals and protozoans. (flagellated, ciliary, amieboid, gliding) Reproduction Simple fragmentation Complex, meosis present, also by or binary fission, no fragmentation, binary fission and meosis, asexual spores in some plants. Algae spores produced in and fungi and few protozoans. some. Genetic Present in some but recombination chromosomal cross over absent. By chromosomal cross over during meiosis.