Cell Structure

Chapter 5

Cells

•Plasma Membrane - Encloses cell

–Phospholipid bilayer

•Transport Proteins

•Receptor Proteins

•Nucleus = DNA.

•Cytoplasm - Semi-fluid matrix filling cell interior.

Cell Theory

•Organisms composed of one or more cells.

–Metabolism and heredity occur within cells.

•Cells are basic units of organization for all organisms.

•Cells arise by division of previously existing cell.

Cells Are Small

•Increases surface area-to-volume ratio.

–Volume increases much more rapidly than surface area with growth of cell.

•Sphere

–Volume = 4/3 πr³

Surface = 4πr²

–Cell membrane partially regulates cell function.

•Small cells have more surface area per unit volume

Prokaryotic Cells

•Bacterial cells (prokaryotic) smaller than Eukaryotic

–cytoplasm

–plasma membrane

–rigid cell wall.

•Gram Positive - Thick, single-layered cell wall.

•Gram Negative - Multilayered cell wall.

–Propelled by flagellum (flagella).

–Little internal organization.

Eukaryotic Cells

•Organelles - Membrane-bound structures, compartmentalize cell, allow multiple simultaneous biochemical reactions

–Vesicles - Storage and Transport

–Nucleus - DNA

–Cytoskeleton - Internal Structure

–Central Vacuole - Storage (Plants Only)

Nucleus

•Stores genetic information.

–Phospholipid bilayer membrane

•Transmembrane proteins permit passage of material in and out of cell.

–DNA in chromosomes.

•Chromatin

Endoplasmic Reticulum

•Internal membrane, phospholipid bilayer and embedded proteins.

–Folded, weaves through cell

•Rough ER - covered with ribosomes.

–Synthesizes proteins.

•Smooth ER - few embedded ribosomes, enzymes for lipid synthesis, detoxification

Golgi Apparatus

•Interconnected flattened membranes (Golgi bodies).

–Collection, packaging, and distribution of macromolecules

–Cis face - Receiving end

–Trans face - Discharging end

Vesicles

•Lysosomes - digestive vesicles from Golgi apparatus.

–Degrading enzymes.

•Break down old organelles, other structures.

Ribosomes

•Ribosomes = protein synthesis.

–rRNA bound within complex of proteins.

–2 subunits.

•Form functional ribosome w/ mRNA.

–Assembled in nucleolus

Mitochondria

•Contain single circular DNA molecule

•Morpholigically similar to aerobic bacteria

–smooth outer membrane and folded inner membrane

–Partition into matrix and intermembrane space.

•Found in most eukaryotes (plant, animal, fungi, protista)

•Powerhouse of cell – aerobic respiration

Chloroplasts

•Contain single circular DNA molecule

•Morphologically similar to photosynthetic bacteria

–Double membrane

–Grana - Stacked membranes internally

•contain light-capturing pigments used in photosynthesis

–Chlorophyll - green

•Make food for the cell

Chloroplast Structure

Centrioles

•Barrel-shaped, near nuclear membrane.

–Help w/ cell division

–Some w/ DNA.

Cytoskeleton

•Network of protein fibers provides cell shape.

–Actin Filaments

–Microtubules

–Intermediate Filaments

Cell Movement

•Within cell – golgi apparatus, motor molecules

•Flagellum - nine microtubule pairs surrounding two central mictotubules.

•Cilia - Short cellular projections often organized in rows.

–Similar to flagella.

–Many functions.

Plant Cells

•Central Vacuole - storage center, increases surface-to-volume ratio

•Cell Walls

–Primary Walls

–Middle Lamella

–Secondary Walls

Endosymbiosis

•Some eukaryotic organelles likely evolved by endosymbiosis.

–A Eukaryotic cell engulfed a prokaryotic cell without digesting it

–Both appear to have benefited from the relationship

•Example: Mitochondria

–Much high energy “waste” in cytoplasm of Eukaryote

–Much ATP produced by Mitochondrion

–All cells w/ endosymbiotic organelles descended from single Eukaryotic cell that ingested prokaryote “ancestor” of organelle