The Cell Summary
The Cell Theory:
●The cell theory states:
○Cells are the fundamental units of life
○All organisms are composed of cells.
○All cells come from preexisting cells.
Why Cells are small:
●Cells size is limited by surface area to volume ratio
○Volume of a cell determines the amount of chemical activity it carries out per unit of time
○Surface Area of a cell determines the amount of substances the cell can take in and the amount of waste product it can release
Prokaryotic vs. Eukaryotic
Compartmentalization
Compartmentalization is vital in the functioning of eukaryotic cells. Compartmentalization separate different processes into organelles increasing the efficiency of reactions within a cell.
Organelles
●Cell Membrane (Plasma Membrane)- is composed of phospholipids with hydrophobic and hydrophilic ends and contain proteins embedded within them. Providing:
○Constant internal environment
○Selectively permeable barrier
○Communication with adjacent cells and receiving extracellular signals
●Cytoplasm- region between the nucleus and cell membrane. Consists of the cytosol and ribosomes
○Cytosol- consists mostly of water with dissolved ions, small molecules, and soluble macromolecules
●Cell Wall- found in plant cells and prokaryotes. Composed of long chains of cellulose. Prevents cells from bursting.
●Nucleus- contains DNA of the cell and the nucleolus
○Nucleolus- where ribosomes are synthesized and assembled
●Nuclear envelope- consists of two membranes with perforations called nuclear pores, where RNA and proteins enter and leave the nucleus
●Peroxisomes- Similar to (but smaller than) lysosomes, the metabolic functions of peroxisomes include:
○Breakdown of fatty acids by beta-oxidation
○Breakdown excess purines to urea
○Breakdown of toxic compounds e.g. in the cells of the liver and kidney.
●Centrioles- Made up of microtubules. Key in nuclear division.
●Ribosomes- Sites of protein synthesis. Two kinds of ribosomes.
○“Free” Ribosomes- suspended within the cytosol. Synthesizes proteins to be used within the cell
○“Bound” Ribosomes- attached to Rough ER. SYnthesizes proteins that are exported outside cell
●Rough Endoplasmic Reticulum- Consists of many interconnected membranous sacs called cisternae . Entry site for most proteins. Contains attached ribosomes. Adds carbohydrates chains to incoming proteins
●Smooth Endoplasmic Reticulum- lacks attached ribosomes, metabolizes carbohydrates, detoxifies drugs and poisons, and synthesizes lipids
●Golgi Apparatus- where proteins are brought from Rough ER by transport vesicles and are modified, packed, and exported out the cell through secretory vesicles
●Mitochondria- Found in animal cells. Double membraned. Site of cellular respiration
●Chloroplast- Found in plant cells. Double membraned. Site of photosynthesis
●Vacuoles- Membrane bound sacs that store material. Usually larger in plant cells
●Lysosomes- membrane bound sacs that contain digestive enzymes which hydrolyze macromolecules into their monomers
●Cytoskeleton- provides structural support and mobility for a cell. Composed of three filaments
○Microtubules- Made of tubulin, involved in cell movement and provide tracks for organelle movement
○Intermediate Filaments- More permanent filaments and reinforce cell shape.
○Microfilaments- Made of actin and are involved in muscle contraction and localized cell contractions
●Cilia/Flagella: Arranged in a 9+2 arrangement of microtubules. Cilia are smaller and more abundant in cells move in a ora-like motion. Flagella are longer and less abundant ( Move in a snake-like motion)
●Vesicles- Transport and delivery of their contents (e.g. molecules such as hormones or neurotransmitters) either into or out of the cell, in both cases via the cell membrane.
○Exocytosis - movement of the contents of secretory vesicles out of the cell.
○Endocytosis - movement of the contents of secretory vesicles into the cell.