Animal Cells

Animal cells are eukaryotic cells, which are enclosed by a plasma membrane and which contain a membrane-bound nucleus and many types of "organelles." Human beings are made up of trillions of these cells!


HOW DO ANIMAL CELLS DIFFER FROM PLANT CELLS?

Cell Walls
Additionally, unlike the cells of plants and fungi, animal cells have no rigid cell wall. The cell walls of plants are composed of celllose, which allows plants to more easily absorb and retain water. The cellulose is strong enough to handle a high degree of water pressure upon the cell wall. Animal cell walls are made up of a permeable plasma membrane.

Photosynthesis
Another big difference between animal and plant cells is that plants have chloroplasts which allow them to use sunlight to photosynthesize their own food. Animal cells don't have chloroplasts and must eat food, which their cells can then use to make energy and reproduce. This process takes place in the mitochondrion of the animal cells.

Vacuoles
Plant cells have one large vacuole, comprising most of the cell, which serves to hold and secrete both waste and nutrients. Animal cells have many smaller vacuoles within each cell.

Collagen vs. Pectin
Animal cells are bound together by a protein known as collagen. Plant and fungal cells are bound together by other molecules, such as pectin.


ANIMAL CELLS - BASIC STRUCTURE
In addition to their nucleus, animal cells also contain additional tiny cellular structures called organelles. These organelles carry out the various functions need for the cell to remain healthy.

Cell Membrane - a permeable plasma membrane which allows the cell to absorb nutrients and excrete waste.

Centrioles - self-replicating organelles that organize the assembly of microtubules during cell division

Cilia - an arrangement of microtubules creating hair-like appendages on the cell surface which assist in the locomtion of the cells.

Cytoplasm - the gel-like substance that fills the cell. It is here that the nutrients are used.

Endoplasmic Reticulum - a large network of membranes which make up more than half of the cell membrane. There are two types of ER, "smooth" ER and "rough" ER. Smooth ER lacks ribosomes on the cytoplasmic surface, while rough ER has ribosomes studding the surface. Rough ER synthesizes and secretes serum proteins (like albumin) in the liver and hormones and other substances in the glands. Smooth ER is involved in the systhesis of phospholipids, is where the breakdown of toxins and carcinogens in the liver, the conversion of cholesterol into steroids, and the release of calcium ions inthe muscles. The smooth ER also transports the products of the rough ER to other parts of the cell, most notably the Golgi Body.

Endosomes - membrane-bound vesicles that are found in almost every animal cell. Through a process known as endocytosis, these organelles work to surround macromolecules or other matter diffusing through extracellular fluid. Theough a process known as exocytosis, the cells secrete matter

Flagella - an arrangement of microtubules, somewhat longer than cilia, that make up the locomotive appendages that are seen on some cells.

Golgi Complex - consists of flattened membranous sacs that are responsible for manufacturing, storing and shipping certain cellular products. It is here that the products of the endoplasmic reticulum are modified and sorted and then sent to their destination.

Lysosomes - membrane-enclosed sacs of enzymes the cell uses to digest cellular macromolecules such as nucleic acids.
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Microfilaments - straight, solid rods made of globular proteins called actin that work together with microtubules to form the framework within the cell known as the cytoskeleton, which reinforces the cell's shape and functions in cell movement.

Microtubules - straight, hollow cylinders that work together with microfilaments to form the framework within the cell known as the cytoskeleton, which reinforces the cell's shape and functions in cell movement.

Mitochondria - convert energy to forms that the cells can use and are the sites where cellular respiration take place.

Nucleus - a membrane-bound structure that is the "brain" of the cell which contains most of the genes that control the cell. The nucleus is enclosed by the nuclear envelope which keeps its contents separate from the cytoplasm. Inside the nucleus is a substance called chromatin which organizes DNA and proteins. When the cell begins reproduction, the chromatin thickens and becomes the separate structures known as chromosomes.

Nucleolus - a structure within the nucleus that helps in the synthesis of ribosomes

Nucleopore - a small hole within the nuclear membrane that allows nucleic acids and proteins to move into and out of the nucleus.

Peroxisome - a specialized metabolic compartment contained by a single membrane. The perosixomes contain enzymes that transfer hydrogen from various substrates to oxygen.

Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly

Vacuole - fluid-filled, membrane-surrounded cavities inside a cell. The vacuole fills with food being digested and waste material that is on its way out of the cell.