Cell Energy, Mitochondria, and Cytoskeleton Quiz

Plasma Membrane

• The plasma membrane is a selectively permeable barrier controlling the passage of substances in and out of the cell
• It is a double layer of phospholipids with embedded proteins, providing a physical barrier separating the inside and outside of the cell
• Phospholipids have a hydrophobic region and hydrophilic polar heads, arranged in a double layer with their tails facing each other
• Plasma membrane proteins mediate the movement of hydrophilic substances and are often amphipathic, having both hydrophilic and hydrophobic regions
• Integral proteins are embedded (partially or fully) into the membrane

Transmembrane Proteins

• Transmembrane proteins are integral membrane proteins that fully span the entire membrane, contacting both extracellular and cytoplasmic areas
• They carry out various functions, such as:
  • Channels and transporters, which can be general or selective, gated or not
  • Carrying out chemical reactions, either alone or as part of a team of enzymes
  • Acting as receptors for external signaling molecules

Cellular Organelles

• Major organelles include:
  • Nucleus
  • Endoplasmic Reticulum (smooth and rough)
  • Golgi apparatus
  • Lysosomes
  • Mitochondria
  • Ribosomes
• The endomembrane system includes the plasma membrane, along with the above organelles, working together to package, label, and ship molecules

Golgi Apparatus

• The Golgi apparatus is a series of flattened sacs or cisternae that contain enzymes of different functions
• Proteins move from the cis to trans side of the Golgi, maturing at the exit cisternae, and then travel to their destination
• Modifications occur within each sac, including the formation of glycoproteins, glycolipids, and lipoproteins

Lysosomes

• Lysosomes contain powerful digestive enzymes and are formed from the Golgi membrane
• They have a membrane that pumps H+ ions to maintain an acidic pH, protecting the rest of the cell from digestion
• Lysosomes are responsible for the digestion of:
  • Substances that enter the cell
  • Cell components, such as organelles (autophagy)
  • Entire cells (autolysis)

Mitochondria

• Mitochondria are responsible for generating ATP through cellular respiration
• They are made up of an outer mitochondrial membrane, an inner mitochondrial membrane with folds called cristae, and a fluid-filled interior cavity called the mitochondrial matrix
• Mitochondria have a separate small genome encoding mitochondrial-specific products
• The number of mitochondria present in a cell is directly related to the amount of energy required by the cell

Cytoskeleton

• The cytoskeleton is a structural support system of the cell, providing shape, size, and integrity
• It is composed of three types of fibers:
  • Microfilaments (diameter: ~7 nm, composed of actin molecules)
  • Intermediate filaments (diameter: 8-12 nm, composed of diverse materials)
  • Microtubules (diameter: 25 nm, composed of tubulin dimers)
• The cytoskeleton acts as scaffolding across the cell and is involved in intracellular transportation and cell movement

Nucleus

• The nucleus is the largest distinct structure inside the cell, enclosed by a double lipid bilayer called the nuclear envelope
• It is continuous with the rough Endoplasmic Reticulum and has nuclear pores that regulate the movement of substances in and out
• The nucleus contains DNA, which is wrapped around histones to form nucleosomes, and is responsible for:
  • Housing and protecting DNA
  • Making RNA and assembling ribosomes
  • Regulating the movement of substances in and out of the nucleus

Cell Theory

• All living organisms are composed of one or more cells
• The cell is the basic unit of structure and organization
• All cells arise only from pre-existing cells
• Universal similarities between cells include:
  • DNA as the heritable material
  • RNA as a messenger
  • Proteins as the workers
  • ATP as an energy source

Prokaryote vs. Eukaryote Cells

• Prokaryote cells lack a membrane-bound nucleus and are typically smaller than eukaryote cells
• Eukaryote cells have membrane-bound organelles and are generally larger than prokaryote cells
• Both types of cells have plasma membranes, cytosol, DNA, RNA, proteins, and ribosomes