Chapter 4 (Campbell's Biology in Focus)

Internal Membranes and Functions

• ==Cytosol== is the semifluid, jellylike substance inside cells

• In eukaryotic cells, most of the DNA is found in the ==nucleus==

• In prokaryotic cells, DNA is focused in a region called the ==nucleoid== which is not membrane enclosed

• The interior of either type of these cells is called cytoplasm

• At the boundary of every cell the ==plasma membrane== functions as a selective border that allows oxygen, nutrients, and wastes to service the entire cell

  • the plasma membrane consists of a double layer of phospholipids

• ==Microvilli== increase the surface area of an object due to the crevices

• The nucleus contains most of the genes in a eukaryotic cell

• The ==nuclear envelope== encloses the nucleus separating its contents from the cytoplasm

  • the two membranes are each a lipid bilayer associated with proteins

  

• The nuclear side of the envelope is lined by the ==nuclear lamina==

• DNA is organized into discrete components called ==genes==

• The complex of DNA and proteins making up chromosomes is called ==chromatin==

• A prominent structure in the nondividing nucleus is the ==nucleolus== (plural of nucleoli) which is a mass of densely stained granules and fibers adjoining part of the chromatin

• ==Ribosomes== are complexes made of ribosomal (RNA) proteins

  • They carry out protein synthesis

Endomembrane System

• Many of the different membrane-bounded organelles of the eukaryotic cell are part of the ==endomembrane system,==

  • the endomembrane system includes the
  • nuclear envelope
  • endoplasmic reticulum
  • Golgi apparatus
  • lysosomes
  • various kinds of vesicles and vacuoles
  • plasma membrane.

• The ==endoplasmic reticulum== is a large network of membranes that accounts for more than half of the plasmic membranes in eukaryotic cells

  • ==Smooth ER== lacks ribosomes
  • ==Rough ER== is studded with ribosomes on the outer surface of the membrane

  

Functions of Rough ER

• Most secretory proteins are ==glycoproteins==
• ==Transport Vesicles== are vesicles in transit from one part of the cell to another

The Golgi Apparatus: the shipping and receiving center

• After leaving the endoplasmic reticulum in transport vesicles, they head to the Golgi Apparatus

  • The ==Golgi Apparatus== is like a warehouse for receiving, sorting, shipping, and some manufacturing.

• A ==lysosome== is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest macromolecules

• ==Phagocytosis== is the process of engulfing smaller organisms or food particles

  • The food vacuole formed through this then fuses with a lysosome

  

  

• ==Vacuoles== are large vesicles formed by the endoplasmic reticulum and Golgi Apparatus

• ==Food Vacuoles== are formed by phagocytosis

• Many unicellular protists living in freshwater have ==contractile vacuoles== that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell.

• Mature plants generally contain a ==central vacuole==, which develops by the coalescence of smaller vacuoles

• The ==endosymbiont theory== states that an early ancestor of eukaryotic cells engulfed an oxygen-using non-photosynthetic prokaryotic cell. Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont.

• The inner folds of a phospholipid bilayer are called a ==cristae==

• The ==cytoskeleton== is a network of fibers extending throughout the cytoplasm

• Eukarya have ==microtubules==, hollow rods constructed from a globular protein called tubulin

• In animal cells, microtubules grow out of a ==centrosome==, a region that is often located near the nucleus and is a “microtubule organizing center”

• Within the centrosome is a pair of ==centrioles==, each composed of nine sets of triplet microtubules arranged in a ring

  • In eukaryotes, a special arrangement of microtubules results in the beating of the flagella and cilia

• The microtubule assembly of a cilium or flagellum is anchored in the cell by the basal body

• Bending involves large motor proteins called dynein

• ==Microfilaments== are thin, solid rods. They are also called actin filaments because they are built from molecules of actin.

• Thousand of actin filaments and thicker filaments of a motor protein called ==myosin== interact to cause a contraction in a muscle cell

• ==Intermediate filaments== are named for their diameter, which is larger than the diameter of microfilaments but smaller than that of microtubules