Cell Structure

7.2 Cell Structure Two major parts: nucleus and cytoplasm Cytoplasm: portion of cell outside of nucleus Prokaryotes have a cytoplasm, but no nucleus There are many parts to the cell The structures are called organelles because they act like specialized organs

Cell as a factory Different organelles can be compared to the machines and assembly lines of a factory

The Nucleus The nucleus serves as the main office/ control center of factory The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules Prokaryotes have DNA with same type of instructions

The Nucleus structure Surrounded by a nuclear envelope made of 2 membranes Nuclear pores Chromosomes Chromatin: a complex of DNA Nucleolus

Organelles that store, clean up and support Many organelles have specific functions Some functions include storage, clean up and support Vacuoles, lysosomes and cytoskeleton

Storage space: Vacuoles Many cells contain large, saclike, membrane enclosed structures called vacuoles Vacuoles store materials like water, salts, proteins and carbohydrates Plants usually have a large central vacuole Also found in some unicellular organisms and animals

Storage space: Vesicles Almost all eukaryotic cells contain smaller membrane enclosed structures called vesicles These store and transport materials between organelles and to and from the cell surface

Clean up crew: Lysosomes Lysosomes are small organelles filled with enzymes. They break down lipids, carbs and proteins into smaller pieces that the rest of the cell can use Also break down old organelles Malfunctioning can cause diseases Found in animal cells and in some specialized plant cells

Support structures: Cytoskeleton The cytoskeleton is a network of protein filaments that helps the cell maintain its shape and is involved in movement Acts like conveyor belts to transport materials Microfilaments and microtubules

Microfilaments Microfilaments are threadlike structures made up of actin protein Form extensive networks for support Help cell move Assembly and disassembly of microfilaments allow cell movement

Microtubules Microtubules are hollow structures made up of tubulin proteins Maintain cell shape Form mitotic spindle Help build projections of cell surface called cilia and flagella Arranged in “9+2” pattern Cross-bridges use chemical energy Centrioles are also made of tubulin and are located near the nucleus to help organize cell division (in animal cells only)

Organelles that build proteins Proteins are important molecules essential for cell function Catalyze chemical reactions Make up important structures Together, ribosomes, the endoplasmic reticulum and the Golgi apparatus synthesize, modify, package, and ship proteins

Ribosomes Proteins are assembled on ribosomes Ribosomes are small particles of RNA and protein found throughout the cytoplasm in all cells Follow coded instructions that come from DNA

Endoplasmic Reticulum The endoplasmic reticulum (ER) is an internal membrane system found in eukaryotic cells Where lipid components of membrane are made Also makes proteins and other materials that are exported from cell

Types of Endoplasmic Reticulum The rough ER is the portion involved in the synthesis of proteins Called rough because of ribosomes on outside Proteins made on the rough ER may be targeted for export to the cell membrane, or to specialized locations within the cell

Types of Endoplasmic Reticulum The other portion of the ER is the smooth ER For many cells the smooth ER contains enzymes that perform specialized tasks Such as synthesis of membranes and detoxification of drugs

Golgi Apparatus The Golgi apparatus is an organelle that modifies, sorts, and package proteins and other materials from the ER for storage in the cell or release outside the cell Acts like the post office

Building Proteins

Organelles that capture and release energy All living things require a source of energy How do cells get energy?

Chloroplasts Chloroplasts are present in plants and some other organisms Chloroplasts capture the energy from the sunlight and convert it into food that contains chemical energy via photosynthesis Two membranes Pigment chlorophyll contained inside

Mitochondria: The cell power plant Mitochondria are present in most eukaryotic cells Mitochondria convert the chemical energy stored in food into compounds that are more convenient for the cell to use Two membranes Inherited maternally Both chloroplasts and mitochondria contain their own genetic information in small DNA molecules

Cellular Boundaries All cells are surrounded by a cell membrane. Many cells also produce a strong supporting layer around the membrane known as a cell wall

Cell walls The main function of the cell wall is to support, shape and protect the cell Animal cells do not have cell walls Many cell walls are porous which allows water, gases and certain substances pass through easily Provides the strength needed by plants

Cell membranes Most cell membranes are made up of a double-layer sheet called a lipid bilayer The cell membrane regulates what enters and leaves the cell and also protects and supports the cell

Properties of Lipids Lipids have oily fatty acid chains attached to chemical groups that interact strongly with water Fatty acid is hydrophobic Opposite end is hydrophilic Hydrophilic head are exposed to outside of cell while fatty acids form an oily layer in the membrane

The Fluid Mosaic Model Protein molecules are embedded in the lipid bilayer in most cell membranes Carbohydrates are attached to many of these proteins Called a “mosaic” because proteins float around the bilayer with many kinds of molecules Some are channels and pumps Some act as identification cards

Selective permeability Some substances are too large or charged to cross the lipid bilayer If a substance can cross a membrane is it permeable to it It is called impermeable it if cannot cross Most biological membranes are selectively permeable Some cross, some don’t

Questions?