Cell Structure and Function Chapter 4

Cell Theory All organisms are made up of cells. In 1830s, Matthias Schleiden (plants) and Theodor Schwann (animals) Cells are the smallest (basic) units of living matter; the structural and functional units of all organisms. Cells are capable of self-reproduction and come only from preexisting cells.

How Big Interactive Illustration

Cell Size Why are Cells so small???

Cell Size Surface-area-to-volume ratio requires that cells be small. Cells need surface area of plasma membrane large enough to adequately exchange materials. As cells get larger in volume, relative surface area actually decreases.

Surface-area-to-volume ratio requires that cells be small. Cells need surface area of plasma membrane large enough to adequately exchange materials. As cells get larger in volume, relative surface area actually decreases.

Surface-area-to-volume ratio SA/V = 3 4 SA/V = 1.5 SA/V = 6 2 1 4 1 4 16 1 2 1 2 Surface Area=1x6=6 Surface Area=4x6=24 4 Volume=1x1x1=1 Volume=2x2x2=8 Surface Area=16x6=96 Volume=4x4x4=64 Surface Area= 24 Surface Area=6 Volume=1 6 1 = Surface Area=96 96 = Volume=1 8 = Volume=64 64

Eukaryotic Cells Cells of organisms belonging to kingdoms Fungi, Animalia, Plantae, and Protista. Membrane-bounded organelles: Ex. nucleus houses DNA in threadlike structures called chromatin. Similar to prokaryotic cells, eukaryotic cells have a plasma membrane and cytoplasm including ribosomes.

Chromatin is a threadlike material that coils into chromosomes just before cell division occurs; contains DNA, protein, and some RNA. Chromosomes are rodlike structures formed during cell division; coiled or folded chromatin.

Nuclear pores (100 nm) permit passage of proteins into nucleus and ribosomal subunits. The nucleus is the site of DNA and determines characteristics of the cell by coding for proteins Nucleoplasm is semifluid medium of nucleus. Nucleoli are dark-staining spherical bodies in nucleus; sites where rRNA joins proteins to form ribosomes. Nuclear envelope is a double membrane that separates nucleoplasm from cytoplasm.

Ribosomes are composed of a large and a small subunit. Each subunit is made of proteins and rRNA. Polyribosomes are several ribosomes synthesizing same protein Ribosomes coordinate assembly of amino acids into polypeptide chains (i.e., protein synthesis). Ribosomes attached to ER depend on an ER signal sequence to bind to a receptor protein.

Nucleus, Ribosomes, & ER Figure 4.9

The Endomembrane System Endomembrane system is a series of intracellular membranes that compartmentalize the cell. Endoplasmic reticulum Rough ER Smooth ER Golgi apparatus Lysosomes Vacuole

Endoplasmic Reticulum Endoplasmic reticulum (ER) is system of membrane channels continuous with outer membrane of the nuclear envelope. Rough ER is studded with ribosomes on cytoplasm side; site where proteins are synthesized and enter the ER interior for processing and modification. Smooth ER is continuous with rough ER, but lacks ribosomes; site of various synthetic processes, detoxification, and storage; smooth ER forms transport vesicles

Endoplasmic Reticulum

Golgi Apparatus Golgi apparatus consists of a stack of 3–20 slightly curved saccules. Vesicles formed from membrane of outer face of the Golgi apparatus then move to different locations in cell; at plasma membrane, they discharge their contents as secretions. Vesicle fuses with membrane of Golgi apparatus or moves to outer face after proteins repackaged. Golgi apparatus receives protein-filled vesicles that bud from the ER.

Lysosomes Lysosomes are membrane-bounded vesicles produced by Golgi apparatus and contain digestive enzymes. Macromolecules enter a cell by vesicle formation; lysosomes fuse with vesicles and digest contents. White blood cells that engulf bacteria use lysosomes to digest bacteria. Autodigestion occurs when lysosomes digest parts of cells.

Peroxisomes Peroxisomes are abundant in liver; Peroxisomes are membrane-bounded vesicles that contain specific enzymes. Peroxisomes are abundant in liver; form hydrogen peroxide (H2O2) broken down by catalase. H2O2  H2O & O2

Vacuoles A vacuole is a large membranous sac; vesicles are smaller than vacuoles. Plant cell vacuoles (usually one or two) are water-filled and give support to cell. Plant vacuoles store water, sugars, salts, pigments, and toxic substances to protect plant from herbivores. Vacuoles in protozoans include digestive vacuoles and water-regulating contractile vacuoles.

Energy-Related Organelles Chloroplasts Photosynthesis is process by which solar energy is converted to the chemical energy of carbohydrates Mitochondria Cellular respiration is process where chemical energy of carbohydrates is converted to that of ATP, the carrier of energy in cells

Only plants, algae, and certain bacteria are capable of carrying on photosynthesis. Chloroplasts are a type of organelle called a plastid; plastids include amyloplasts, which store starch, and chromoplasts, which contain red and orange pigments.

Mitochondria are bounded by a double membrane; inner membrane has folds (cristae) that project into inner space (matrix) with enzymes that break down carbohydrate-derived products; ATP production occurs at cristae. Mitochondria contain ribosomes and their own DNA that specifies some proteins; other proteins are coded by nucleus DNA. Cell energy is provided by ATP; all organisms carry on cellular respiration and all except bacteria have mitochondria.