Cell Structure and Functions Essay Sample

Cell Structure and Functions Pages
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* 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

SUMMARY OF CELL STRUCTURE AND FUNCTION

* 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

Cells
* Cell theories 3 major principles
* Cell’s 4 common features
* Plasma membrane
* Cytosol
* A thick fluid that fills their interior
* DNA
* 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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