Cell Structure
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Presentation Transcript
Cell Theory • Every living organism is made up of one or more cells • The smallest living organisms are single cells • Cells are the functional units of multi-cellular organisms • All cells arise from preexisting cells
Cell Structure • Basic Features of All Cells • Features of Prokaryotic Cells • Features of Eukaryotic Cells
Cells Share Certain Basic Features • A cell membrane • Nucleic acid • A cytoplasm • Ribosomes
Function of Cell Membrane • Isolates the cell’s contents from external environment • Regulates the flow of materials into and out of the cell (i.e. selectively permeable ) • Allows interaction among cells
Structure of the Cell MembraneFluid-Mosaic Model • Consists of phospholipids and proteins • The head region of each phospholipid molecule “loves” water (i.e. is hydrophilic) • The tail region of each phospholipid “hates” water (i.e. is hydrophobic) • Phospholipids form a bilayer • Proteins are embedded in phospholipid bilayer
Nucleic Acid • Deoxyribonucleic acid (DNA) has two functions: • DNA controls protein synthesis in the cell • DNA is replicated and passed on to progeny cells during reproduction
Cell Cytoplasm • Consists of all materials inside the plasma membrane • It is the “bulk” of the cell • It is the site of cell metabolism: • (1) breaking down complex molecules for energy and simple “building block” molecules • (2) synthesis of new cell structures
Ribosome • Ribosomes are the sites of protein synthesis, where an RNA strand is translated into an amino acid sequence. • Protein synthesis is extremely important to cells, and so large numbers of ribosomes are found throughout cells (often numbering in the hundreds or thousands).
Prokaryotes Eukaryotes
Prokaryotic Cells • Lack a nucleus (though DNA is concentrated in a region called the cell’s nucleoid) • Lack membranous organelles • Are small in size ( < 5 um ) • Many have cell walls • Belong to the Domain Archaea and Domain Bacteria
Eukaryotic Cell • DNA is housed in a membranous organelle called the nucleus • Membranous organelles exist in the cytoplasm and perform specific cell functions • A network of protein fibers called the cytoskeleton give the cell shape and stability • Cells are large in size (10 – 100 um)
Nucleus • Control center of the eukaryotic cell • Nucleus has three distinct parts: • (1) nuclear envelope: double membrane between nucleoplasm and cytoplasm • (2) nuclear pores: openings between nucleus and cytoplasm • (3) nucleoplasm: fluid portion of nucleus that contains DNA and nucleolus
Nuclear Envelope • Nuclear envelope is a double membrane • Isolates cytoplasm from nucleoplasm • Regulates flow of materials between cytoplasm and nucleoplasm • Outer nuclear membrane is continuous with cytoplasm’s endoplasmic reticulum
Nucleoplasm • Contains the hereditary molecule deoxyribonucleic acid (DNA) which always remains in the nucleus • Loose “non-condensed” strands of DNA are called chromatin (cell is not dividing) • Tight “condensed” strands of DNA are called chromosomes (cell is dividing)
Nucleolus • Present inside of nucleus as a distinct region • Consists of ribosomal RNA, protein, ribosomes and DNA • Nucleoli are the sites of ribosome synthesis in the cell
Endoplasmic Reticulum • A complex system of membranes present within the cytoplasm • Endoplasmic reticulum (ER) is continuous with the nuclear envelope and the plasma membrane • ER functions as an internal transport system for the cell
Endoplasmic Reticulum • There are two types of ER: • (1) smooth ER: lacks ribosomes on its surface • Involved in lipid synthesis • (2) rough ER: outside is studded with ribosomes • Involved in protein synthesis
Golgi Complex • A set of specialized membranes derived from the ER • Looks like a stack of flattened sacs or vesicles • Receives contents from ER, modifies these products, and packages them for transport out of cell
Lysosome • A membranous sac (or vesicle) containing digestive enzymes • Enzymes used to break down complex molecules in the cell • Lysosomes’ enzymes derived from RER and lysosome’s sac derived from Golgi complex
Vacuole • Membranous sac used for storage of water, waste, nutrients in the cell • Plant cells tend to have one, large vacuole • Animal cells tend to have numerous, small vacuoles
Peroxisome • Similar to lysosome • Membrane-bound vesicle that contains enzymes • Enzymes are used to breakdown toxic substances to hydrogen peroxide • Hydrogen peroxide is broken down by catalase to produce water and oxygen
Mitochondrion • Double membrane organelle • Outer membrane is smooth • Inner membrane is highly folded (in order to increase inner surface area for cellular respiration) • Folds are called cristae (sing. crista) • Inner fluid portion of mitochondrion is called the matrix
Mitochondrion • Space between inner and outer membrane is called the intermembrane compartment • Function of mitochondrion is the breakdown of complex molecules to release energy for the cell (cellular respiration) • All eukaryotic cells have mitochondrion
Chloroplast • Present only in plants • Site of photosynthesis • Double membrane system encloses the fluid-filled space called the stroma • Membrane system within stroma is organized into interconnected, flattened sacs called thylakoids
