CELL ORGANELLES Functions

CELL WALL – PLANT CELL ONLY

! The cell walls of plants provide strength and protection, keeping the cells from bursting or rupturing.

! They also protect against insects and parasites, and keep cells hydrated.

! Some cell walls are relatively thick, providing structural support for the plant, while others are thinner in order to promote cell-to-cell transfer and communication.

PLANT CELL WALL

CELL MEMBRANE

! The primary function of the cell membrane is to encapsulate the cell’s contents. It contains all of a cell’s structures within it.

! Its secondary functions include regulating what molecules and substances can enter and exit the cell and its water balance.

! There are five ways molecules and substances can enter or leave the cell as it performs the central function of the cell membrane. !  Three of these means are passive and two are

active. The passive means of transportation are lipid diffusion, osmosis and passive transport.

!  The two active means are active transport and vesicles.

CELL MEMBRANE

CYTOPLASM

! Cytoplasm's primary function is to act as a medium of suspension for a cell's organelles, keeping a cell's inner structure intact.

! A secondary, but no less important, function of cytoplasm is to act as a means of transport for materials the cell uses and produces.

! The final function of cytoplasm is to offer protection. !  All cells experience movement in one form or

another. !  Contact with other cells or outside surfaces is all

but certain. !  The cytoplasm acts as a buffer in these cases,

protecting organelles from the shock of impact.

NUCLEUS ! It controls the heredity characteristics of an

organism. ! It is responsible for protein synthesis, cell

division, growth, and differentiation.  ! The nucleus stores heredity material in the form

of deoxyribonucleic acid (DNA) strands. It stores proteins and ribonucleic acid (RNA) in the nucleolus. 

! It is a site for transcription, a process in which messenger RNA (m RNA) are produced for protein synthesis.

! It aids in exchange of DNA and RNA (heredity materials) between the nucleus and the rest of the cell.

NUCLEOLUS

! The primary function of the nucleolus is to make ribosomes, which act as workhorses to transcribe information from deoxyribonucleic acid (DNA).

! The size of the nucleolus can vary depending on the type of cell it is in.

! Each adult human cell can have only one nucleolus, although different species of eukaryotes have varying numbers.

CHROMATIN ! Chromatin is DNA in the nucleus of a cell that has been

condensed and sometimes modified into a relatively inactive state.

! The majority of most human DNA exists in this condensed state at any given time, which allows its over six-foot length to fit within the microscopic confine of the nucleus.

! Accessing DNA that has been condensed into chromatin is often a two-fold process, involving reorganization of the condensed DNA and removal of any modifications that previously signaled condensation.

! The release of condensed DNA is called chromatin remodeling and can happen very quickly, usually in thousandths or millionths of a second.

ROUGH ENDOPLASMIC RETICULUM

! The rough endoplasmic reticulum (rough ER) is a complex membrane-bound organelle and is involved in the transport of the proteins made by ribosomes on its surface.

! Shaped like a three dimensional continuous maze, the rough ER is a system of membranes that extends from the nucleus of the cell to the cell membrane.

! As the protein is produced, it is moves into the interior of the organelle, where it awaits transport.

! Another function of the rough endoplasmic reticulum is the modification of some of the proteins produced by the ribosomes.

SMOOTH ENDOPLASMIC RETICULUM

! One of the primary functions of the smooth endoplasmic reticulum is to produce and move lipids, an essential component of a cell's outer membrane, and steroids.

!  Another function it performs in all cells is the final production of glucose, an energy storage molecule.

! The smooth endoplasmic reticulum also metabolizes natural and ingested toxins.

RIBOSOMES

! The function of a ribosome is the manufacture of proteins in biological cells using RNA and amino acids.

!  In microbiology, the function of a ribosome is to "read" the information contained in the mRNA while creating proteins.

! The function of a ribosome is to build an amino acid chain which will create a specific form of protein.

!  It does so by "reading" the genetic instructions contained in the mRNA. The two ribosome subunits combine and lock onto the mRNA to begin the protein-building process.

LYSOSOMES

! A lysosome is a structure inside an animal cell which breaks down materials into compounds which can be used or discarded by the cell, as needed. !  Each lysosome produces an assortment of

digestive enzymes which it uses to break down food and waste material.

! Lysosomes also play other important roles in cell upkeep, ranging from consuming worn-out structures within the cell to attacking foreign bacteria before it has a chance to penetrate the cells.

GOLGI COMPLEX

! The function of the Golgi body includes sorting and processing proteins and assist in the distribution of lipids.

! After proteins are assembled in the rough endoplasmic reticulum, they travel to the Golgi body for processing and distribution throughout the cell or to an extracellular destination.

! Once in the Golgi body, the proteins travel from region to region and may be modified by the enzymes contained in each region.

! Eventually, the protein reaches the trans-Golgi where it is sorted and packaged for distribution.

! Golgi vesicles are released from the apparatus to transport the finished proteins to their final destinations.

CHLOROPLAST – PLANTS ONLY

! A chloroplast is a type of structure, called an organelle, that is found in plants and is where photosynthesis occurs.

! Normally present in plant leaves, chloroplasts contain all of the components that allow the plant to convert sunlight into usable energy.

MITOCHONDRIA

! Mitochondria are the cell powerhouse of eukaryotic cells.

! The main function of mitochondria is the production of adenosine triphosphate (ATP) by a process known as cell respiration.

! ATP is a chemical compound that stores energy in the form of chemical bonds.

! Energy is derived from cell nutrients, mostly from glucose and fatty acids, and released whenever it is needed by the energy-requiring functions of cells.

VACUOLES

! Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed.

! The function and significance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants.

VACUOLES ! In general, the functions of the vacuole include:

!  Isolating materials that might be harmful or a threat to the cell

!  Containing waste products !  Containing water in plant cells !  Maintaining internal hydrostatic pressure or

turgor within the cell !  Maintaining an acidic internal pH !  Containing small molecules !  Exporting unwanted substances from the cell !  Allows plants to support structures such as leaves

and flowers due to the pressure of the central vacuole

VACUOLE

Plant Cell

Animal Cell

CYTOSKELETON

! Cytoskeleton is an intricate network of microtubules and microfilaments.

! It spans the cytoplasm to provide support, shape, elasticity, and protection to the contents of the cell, much like the larger skeleton found in many living organisms.

! This structure is made up of proteins which assemble themselves into actin filaments, intermediate filaments, and microtubules.

! One of the key functions of the cytoskeleton is to act as cellular scaffolding, providing support for the contents of the cell and anchoring the nucleus in place.

CYTOSKELETON

! When organelles need to move around inside the cell, they utilize this structure for support. [cytoplasmic streaming]

! The cytoskeleton also enables the cell itself to move with the assistance of tiny projections called cilia.