Cell Structure

Notes Chapter 7.2 “Cell Structure”
Eukaryotic cells can be divided into two regions:  the nucleus and the cytoplasm

• Cytoplasm:  the region of the cell outside the nucleus
• Prokaryotic cells have cytoplasm but no nucleus.
• The nucleus contains nearly all the cell’s genetic information (DNA), and therefore, the code for making proteins and other molecules that the cell needs.
• Surrounded by a porous nuclear envelope which allows substances to move into and out of the nucleus
• Contains chromosomes which carry DNA
• Most contain a nucleolus – responsible for the production of ribosomes

• Organelles:  “tiny organ”, specialized structures inside the cytoplasm

• Vacuoles:  storage areas in a cell (for carbohydrates, waste, water, & proteins)
• in plants the vacuole is usually singular and large (the pressure of the water in the vacuole helps support the leaves and flowers of the plant)
• in single celled organisms (paramecium, euglena) there is a contractile vacuole which expels excess water from the cell
• vesicles – membrane bound organelles in eukaryotic cells that moves materials between organelles and out of the cell

• Lysosomes:  “the clean-up crew” of a cell
• Filled with enzymes
• Break down old organelles, as well as carbohydrates, proteins, and lipids into molecules that can be used by the cell

• Cytoskeleton:  protein filaments that give a cell its shape and help transport materials within a cell
• Microfilaments – made of a protein called actin
• Enable amoebas to move using pseudopods – “false feet” – structures that enable them to “crawl” across a surface
• Microtubules – made of proteins called tubulins
• Make centrioles in animal cells, mitotic spindle, cilia, and flagella
• In cilia and flagella microtubules are arranged in a “9 + 2” pattern that allow the cells to move through their environment
• Cilia and flagella are extensions of the cell surface

• Ribosomes:  structures made of RNA and protein
• responsible for the assembly of protein molecules from DNA’s coded instructions

• Endoplasmic Reticulum: (ER) assembly of lipids, proteins, and other molecules within the cell
• rough ER has ribosomes on the surface that complete the assembly of proteins
• proteins made here are released (secreted) from the cell
• proteins that are made here are membrane proteins and those needed at the lysosomes and in other specialized structures within the cell
• smooth ER has no ribosomes on the surface
• contain enzymes that help create lipids for membrane and detoxify drugs

• Golgi Apparatus:  take proteins made in the rough ER and modifies, sorts, and packages them

• These proteins will be stored or released from the cell

• Chloroplasts:  capture energy from the sun and converts it to food for the organism (in the form of chemical energy)
• This process is called photosynthesis.
• Chloroplasts are surrounded by two membranes.
• Contain the pigment chlorophyll
• Has its own DNA

• Mitochondria:  convert chemical energy of food into compounds that the cells can use
• two membranes – inner one is folded up
• in humans nearly all mitochondria comes from the egg cell
• has its own DNA

• Cell Membrane – controls what enters and leaves the cell, supports and protects the cell
• all cells have a cell membrane
• double-layer called a lipid bilayer allows for flexibility
• fatty acid tails are hydrophobic – “water hating”
• opposite side is hydrophilic – “water loving”
• when mixed with water the fatty acid tails clump together on the inside of the bilayer and the water loving heads attract to the water

• described as a fluid mosaic model – the cell membrane has proteins and carbohydrates embedded in it that float around among the lipids
• proteins are involved in movement of molecules across the membrane (some have channels, others act as pumps)
• carbohydrates act as identification tags so cells recognize each other
• semipermeable (selectively permeable):  describes the cell membrane
• some substances are too large or too strongly charged to pass through the membrane
• other substances can pass into and out of the cell
• Cell wall:  supports, shapes, and protects the cells of certain organisms
• Found in most prokaryotes and all plants
• Provide the strength plants need to withstand gravity
• Porous – allows water, oxygen, carbon dioxide, and some other materials to cross easily
• Cells with a cell wall also have a cell membrane.