General Biology I ORGANIC CHEMISTRY AND CELLS Lecture 7

The Nucleus and Endomembrane System

  • Network of membranes enclosing the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles and finally the plasma membrane

Nucleus

Chromosomes → DNA and proteins

Nuclear matrix
nuclear lamina and an internal nuclear matrix, Filamentous network

Ribosome assembly

  • occurs in the nucleolus

  • A ribosome is composed of a small and a large subunit

  • Ribosomal proteins and RNA molecules enter the nucleolus and are assembled

  • Subunits exit the nucleolus and move to the cytosol


Endoplasmic Reticulum


Rough E R

  • Studded with ribosomes

  • Proteins are packaged into membrane vesicles and moved from one location in the endomembrane system to another

  • Inserts protein into the E R membrane

  • Attaches carbohydrates to proteins and lipids – glycosylation

Smooth E R

  • Involved in metabolism – detoxification, drugs, ethanol

  • Carbohydrate metabolism

  • Storage of calcium ions

  • Lipid synthesis and modification


Golgi apparatus function


Also called the Golgi body, Golgi complex, or simply Golgi


Three overlapping functions

  • Secretion, processing, and protein sorting


Lysosomes
Contain acid hydrolases that perform hydrolysis


Autophagy- self eating


Recycling of worn-out organelles through endocytosis


Vacuoles

  • Functions are extremely varied, and they differ among cell types and environmental conditions

  • Central vacuoles- in plants for storage and support

  • Contractile vacuoles- in protists for expelling excess water

  • Phagocytic vacuoles- in protists and white blood cells for degradation


Peroxisomes

  • Catalyze certain reactions that break down molecules by removing hydrogen or adding oxygen

  • Hydrogen peroxide (H2O2) is a byproduct

  • Catalase breaks down dangerous H2O2 into water and oxygen


Semiautonomous organelles

  • Mitochondria and chloroplasts

  • Grow and divide to reproduce themselves

  • They are not completely autonomous because they depend on the cell for synthesis of internal components


Mitochondria
Primary role is to make ATP


Outer and inner membrane

  • Inner membrane highly folded to form projections called cristae

  • Intermembrane space and mitochondrial matrix


Chloroplasts


Photosynthesis

  • Capture light energy and use some of that energy to synthesize organic molecules such as glucose

Found in nearly all species of plants and algae


Outer and inner membrane

  • Intermembrane space

  • Thylakoid membrane

Chloroplasts specialized version of plastids; all derived from unspecialized proplastids


Endosymbiosis of chloroplast and mitochondrion

  • Endosymbiosis – smaller species lives inside larger species


Protein sorting

  • Remain in cytosol

  • Co-translational sorting

  • Post-translational sorting