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Cell Structure and Functions Essay Sample

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Cell Structure and Functions Essay Sample

* The Cell Theories 3 major principles:
* Cell is the basic unit of life
* All organisms consist of one or more cells
* New cells are created when existing cells divide
* Most cells contain 4 common features:
* A flexible plasma membrane that surrounds the cell
* A thick fluid called cytosol that fills their interior
* The nucleic acid DNA
* Protein structures called ribosomes, which are responsible for making other proteins important for various cell functions
* Plasma membranes:
* Consist of a phospholipid bilayer-
* Two layers of phospholipids arranged so that the hydrophilic heads” in each layer face outwards
* Are fluid: phospholipids are able to move, usually side to side, within a layer
* Plasma membranes contain many other macromolecules:
* A variety of proteins, lipids, and carbohydrates are embedded in a plasma membrane
* Proteins have many functions in the membranes:
* Channels that help the passage of ions or molecules
* Enzymes, which control chemical reactions
* Anchors for other cell structures, such as the cytoskeleton
* Receptors, which bind molecular signals that are important for cell-to-cell communication
* Cholesterol helps maintain membrane fluidity

* Carbohydrates are usually attached to membrane proteins or lipids
* They often act as markers that aid in cell recognition
* Human ABO blood types are determined by carbohydrates present on red blood cell membranes
* Plasma membranes are selectively permeable

* Only certain substances can pass through a membrane
* Generally, a small and uncharged substance can cross unaided
* Substances can diffuse across a plasma membrane
* Atoms and molecules are in constant motion
* Diffusion is the net movement of atoms or molecules from an area of high to an area of low concentration
* Thus, the direction of net movement follows the concentration gradient
* The diffusion of water across a selectively permeable membrane is called osmosis
* Two basic cell types:

* Prokaryotic
* Simply organized because they lack internal structures call membrane bound organelles
* Lacks a nucleus which is a membrane bound organelle * Generally unicellular
* Ex) bacteria
* Main structures:
* Cell wall- additional covering for cell besides plasma membrane. Also more rigid than membrane
* Nucleoid: where DNA is located. Not a true nucleus because DNA is not enclosed in plasma membrane
* Flagellum: protein structure used for cell movement. Different structures than a eukaryotic flagellum
* Eukaryotic

* True nucleus
* More complex organization because they each contain a nucleus an a variety of other organelles
* Can be uni-cellular or multicellular
* Ex) animals, plants, and fungi
* Function: store and protect most of the DNA present in the cell
* Basic structure:
* Surrounded by a nuclear envelope consisting of two layers of plasma membrane
* Within the nuclear envelope is a layer of protein fibers called the nuclear lamina
* Nuclear pores assist with transport into or out of the nucleus
* The Endomembrane System:

* Group of membrane-bound organelles that often work together to make and transport biological macromolecules, like a molecule factory

* Some organelles help to break down macromolecules
* Organelles in the endomembrane system include:
* Smooth endoplasmic reticulum
* Consists of plasma membrane folds that are smooth looking in appearance
* Makes lipids such as phospholipids and steroids
* In muscle cells: store calcium ions to aid muscle contraction
* In liver cells: helps to get rid of drugs and toxins
* Rough endoplasmic reticulum

* Consists of plasma membrane folds with ribosomes docked along the membrane
* Ribosomes thread proteins into the RER
* RER provides a space for these proteins to fold into their proper shape. Folded proteins can be modified while in the RER
* RER also produces some lipids and proteins that are part of the cell membrane
* Molecules from RER are shipped by packaging tem into vesicles , a small bits of RER membrane bud off and carry their cargo to another destination * Golgi apparatus

* Consists of plasma membrane folds that look like a stack of pancakes
* Vesicles deliver biological macromolecules to the side of the Golgi apparatus that acts like a receiving dock
* Lysosomes (and vesicles)

* Vesicles that contain enzymes that are designed to break down biological macromolecules. The enzymes are made by the RER, then processed and packaged by the Golgi apparatus * Many unicellular eukaryotes, such as amoebas, rely upon lysosomes to help break down food particles that have been engulfed by the cells * Mitochondria

* Where most of the process of cellular respiration takes place in eukaryotic cells * Cellular respiration utilizes glucose and O2 to generate energy in the form of ATP * ATP molecules provide energy for a wide variety of cellular functions * a eukaryotic cell can contain up to several hundred mitochondria * Eukaryotic cytoskeleton

* Cells must maintain their shape. Cell shape is regulated by a structure called the cytoskeleton * The e. cell cytoskeleton is
a mixture of 3 different protein fibers: * Microfilaments

* Intermediate filaments
* Microtubules
* E. cells, like single-celled protozoans that live in freshwater ponds, move with help of cilia * Other e. cells, like animal sperm, move with help of flagella * E. cilia and flagella consist of microtubule bundles that are surrounded by the cell’s plasma membrane. They beat back and forth to aid cell movement. Cilia are much shorter than flagella


* most cells contain 4 common features, including a plasma membrane * a plasma membrane consists of a phospholipid bilayer with a variety of other embedded macromolecules. It is a selectively permeable barrier that allows small and uncharged substances to diffuse unaided * prokaryotic cells are simply organized

* eukaryotic cells have complex internal organization made up of various membrane-bound organelles with different functions * many e. organelles are part of the endomembrane system, whose main function is the production and transport of biological macromolecules such as proteins, lipids, and some carbohydrates * a cell has a cytoskeleton that helps it maintain its shape. The cytoskeleton of a e. cell consists of 3 different protein fibers * Some e. cells have cilia or flagella to help with cell movement or feeding. These structures consist of microtubule bundles covered by plasma membrane

* Cell theories 3 major principles
* Cell’s 4 common features
* Plasma membrane
* Cytosol
* A thick fluid that fills their interior
* Ribosome
* Responsible for making other proteins important for various cell functions
* Plasma Membrane:
* Consist of phospholipid bilayer
* Are fluid
* Cholesterol helps maintain membrane fluidity
* Proteins function in membrane:
* Channels that help the passage of ions or molecules
* Enzymes, which control chemical reactions
* Anchors for other cell structures such as cytoskeleton
* Receptors, which bind molecular signals that are important for cell to cell communication
* Selectively permeable

* Generally, a small and uncharged substance can cross unaided
* Substances can diffuse across a plasma membrane
* Diffusion is the net movement of atoms or molecules from an area of high to an area of low concentration
* Diffusion of water is called osmosis
* 2 basic cell types:
* Prokaryotic
* Unicellular
* Simply organized
* Lacks a nucleus which is a membrane bound organelle
* Eukaryotic
* True nucleus
* Multicellular
* Function is to store and protect most of the DNA present in the cell
* Endomembrane System:
* Organelles in e. system include:
* Smooth ER
* Organelle that produces many types of lipids for various cell functions
* Rough ER
* Golgi apparatus
* Lysosomes

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