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