INVESTIGATION 2 Structure and Function of the Cell By: Madison Shelpuk & Connor Erickson

Internal Organization Cells contain a variety of internal structures called organisms. Organelle is a cell component that performs specific functions for the cells. An entire cell is surrounded by a thin membrane, called cell membrane. Inside the cell are a variety of organelles, which are surrounded by their own membranes. Nucleus is the large organelle near the center of the cell. Eukaryotes are organisms whose cells contain a membrane- bound nucleus and other organelles. Prokaryotes are unicellular organisms that lock a membrane- bound nucleus and other organelles.

Cell Membrane Selectively permeable is when the cell membrane controls the ease which substances easily crosses the membrane. The structure of the cell membrane depends on the functions the cell performs. Membrane Lipids One of the major types of liquids in the cell membrane is phosphoric. Cells are bathed in an aqueal or watery environment. Since the inside of the cells is also an aqueous environment, both sides of the cell membrane are surrounded by water molecules.

Membrane Proteins Peripheral proteins are proteins that are attached to the surfaces of the cell membrane. They are located on both the interior surface and the exterior surface of the cell membrane. Integral proteins are proteins that are embedded in the bi- layer. Because the cell membrane is selectively- permeable, cells must have mechanisms for transporting molecules through the lipid bi-layer.

Fluid Mosaic Model of the Cell Membranes Scientists use the fluid mosaic model to describe the cell membrane. The lipid bi-layer behaves more like a fluid than a solid.

Organelles Between the cell membrane and the nucleus lies the cytoplasm, which contains the various organelles of the cell. Cytosol are organelles that are bathed in a gelatin- like aqueous fluid. The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation.

Mitochondria Mitochondria are scattered throughout the cytosol, which are relatively large organelles. Mitochondria are he sites of chemicals reactions that transfer energy from organic compounds to the ATP. Cristae are the inner membrane, that has many long folds. The Cristae greatly enlarge the surface area of the inner membrane, providing more space for the chemical reactions that occur in the mitochondria.

Ribosomes Most numerous organelles in most cells. Unlike most organelles, ribosomes are not surrounded by a membrane. They are made up of proteins and RNA. Inside the cell’s nucleus, proteins and RNA are packaged into ribosomes, which are transported to the cytosol. Some ribosomes remain free within the cytosol, while some become attached to an organelle called the endoplasmic reticulum. Proteins to be used within the cytosol are produced on the ribosomes that are free in the cytosol. Proteins exported from the cytosol are produced on the ribosomes that are attached to the endoplasmic reticulum.

Endoplasmic Reticulum ER is a system of membranous tubules and sacs. ER functions as a path along which molecules move from one part of the cell to another. The amount of ER inside a cell depends on the cell’s activity. A cell usually contains two types of ER: – Smooth ER: Involved in the synthesis of steroids in gland cells, regulation of calcium levels, and breakdown of toxic substances. – Rough ER Prominent in cells that make large amounts of proteins to be exported from the cell.

Golgi Apparatus Golgi Apparatus is the processing, packaging, and secreting organelle of the cell. Golgi apparatus is a system of membranes. Working with the ER, the golgi apparatus modifies proteins for exporting the cell.

Lysosomes Small, spherical organelles that enclose hydrolytic enzymes within single membranes. These enzymes can digest proteins, carbohydrates, lipids, DNA, and RNA. They also digest old organelles, viruses, and bacteria. Lysosomes are common in animals, fungi, and protists, but not in plant cells. Lysosomes play a role during early development in the embryo.

Cytoskeleton The structure of a cell. Not surrounded by membranes. Participates in movement of organelles within the cytosol. There are two major components of the cytoskeleton: – Microfilaments Threads made of a protein called actin Contribute to cell movement and play a role in the contraction of muscle cells. – Microtubles Largest strands, hollow tubes. When a cell is about to divide, bundles of microtubles come together and expand across the cell. These bundles are called spindle fibers which assist in the movement of chromosomes during cell division.

Cilia and Flagella Cilia and Flagella are hairlike organelles that extend from the surface of the cell, where they assist in movement. They can be found in many eukaryotic cells. When these organelles are short and numerous, they are cilia. The movements of cilia propel the tiny organisms through the water to find food or escape from predators. When these organelles are long and less numerous, they are flagella. On many cells, including sperm cells, only one flagella is present. By whipping back and forth, flagella can swiftly propel around.

Nucleus The nucleus is often the most prominent structure within a eukaryotic cell. It maintains it’s shape with the help of the nuclear matrix. The nucleus is surrounded by a double membrane called the nuclear envelope. Inside the nuclear envelope are strands of chromatin, a combination of DNA and protein. When a cell is about to divide, the chromatin strands coil up and become densely packed, forming chromosomes. The nucleus stores hereditary information in its DNA.

Plant Cells - Cell Wall Plant cells are covered by a rigid cell wall that lies outside the cell membrane. It is rigid which helps support and protect the plant. The walls contain long chains of cellulose, which is embedded in proteins and other carbohydrates and harden the entire structure. Pores in the wall allow ions and molecules to exit and enter the cell. When a plant cell is being formed, a primary cell wall develops outside the membrane which may expand more and more and when it reaches full size, a second wall may develop. When you hold a piece of wood, you are touching secondary walls. The cells inside the walls have died and disintegrated.

Vacuoles Vacuoles are another common characteristic of plant cells. Vacuoles are fluid-filled organelles which store enzymes and metabolic wastes. They can store some wastes which are toxic and must be kept away from the rest of the cell.

Plastids Another distinguishing feature of plant cells, the plastids are organelles that are surrounded by two membranes and contain DNA. Some plastids store starch or fats, while others contain pigments, which absorb visible light. The most familiar type of plastid is the chloroplast, which encloses a system of sacs called thylakoids. Chloroplasts convert the energy of sunlight into chemical energy. This conversion occurs during photosynthesis.