Chapter 3 Cell Structure and Function - Biology



Chapter 3 Cell Structure and Function

Chapter 3.1

Robert Hooke was first to identify cells and he named them.

Cell theory

• All organisms are made of cells

• All cells come from existing cells

• The cell is the most basic unit of life

Cytoplasm

• Jellylike substance that contains cellular material such as organelles, proteins, nucleic acids, minerals, and ions

Organelles

• Specialized structures that perform distinct processes within the cell: “mini organs”

• Most organelles are surrounded by a membrane

Prokaryotic Cells – example: Bacteria

• Do not have a nucleus

• Do not have membrane bound organelles

• DNA is suspended in the cytoplasm

• All are microscopic, single-celled organisms

Eukaryotic Cells – example: Plants and animals

• Do have a nucleus

• Do have membrane bound organelles

• May be multicellular or single celled organisms

Chapter 3.2

Cytoskeleton

• The network of proteins that support and shape the cell, aid in transport of organelles inside the cell, aid in cell division, enable cell to move: 3 types

Microtubules (largest of the three)

• Long hollow tubes

• Give cell its shape

• Act as “tracks” for movement of organelles

• When cells divide, microtubules form fibers that pull half of DNA into new cell

Intermediate Filaments (smaller than microtubules)

• Give cell its strength

Microfilaments (smallest of the three)

▪ Enable cells to move and divide

▪ Play important role in muscle cells (ACTIN): help muscles

contract and relax

Nucleus

• Stores and protects the cell’s genetic material (DNA)

• Enclosed in a double membrane called a nuclear envelope that has pores which allow large molecules to pass through between the nucleus and the cytoplasm

Endoplasmic reticulum

• Synthesizes proteins and lipids, both on the surface and inside the lumen

• Interconnected network of thin folded membranes.

• Form a maze of enclosed spaces called lumen

• Connected to the nucleus

It has two types:

• Rough ER: surface covered with Ribosomes – synthesizes proteins

• Smooth ER: no Ribosomes – synthesizes lipids

Lysosomes

• Digest and recycle foreign materials, and break down damaged or worn-out cell parts

• Organelle that contains digestive enzymes (hydrolytic enzymes)

• Defend cell from invading bacteria and viruses

Mitochondria

• Organelle shaped like a bean that provides energy for the cell

• Converts molecules from food into usable energy

• Smooth outer membrane

• Folded inner membrane that greatly increases the surface area: folds called cristae

Vacuole

• A sac filled with fluid inside cell. It stores materials that the cell needs, such as water, food molecules, inorganic ions, and enzymes

• Animal cells contain many small vacuoles

• Central vacuole is a single large sac that usually takes up most of the space in a plant cell.

Vesicle

• A small membrane bound organelle that carries materials from one part of cell to another

• Generally short lived, and are formed and recycled as needed

• Often used in endocytosis and exocytosis

Cell wall

• Found in plant cells, algae, and most bacteria; a rigid layer that gives protection, support, and shape to the cell

• In plants, cell wall made of cellulose

• Cell walls of plants and algae have small openings (channels) to allow water and other molecules small enough to pass through

Chloroplast

• An organelle found in a plant cell that carries out photosynthesis

• Double membrane organelle

• Contain chlorophyll, a light absorbing molecule that gives plants their green color

Golgi apparatus

• Process, sorts and delivers proteins

• Closely layered stacks of membrane-enclosed spaces

Ribosomes

• Form proteins (protein synthesis)

• Made of proteins and RNA

• Assembled in the nucleolus

Centrosome and Centrioles

• Centrosome is small region of cytoplasm that produces microtubules

• In animal cells, contains two small structures called centrioles

• Centrioles are cylinder shaped organelles made of short microtubules arranged in a circle

• Centrioles divide DNA during cell division

Chapter 3.3

Cell membrane

• Forms a boundary between the cell and the outside environment

• Controls what goes into and out of cell

• Consists of a double layer of phospholipids (bilayer)

Phospholipid

• The material that makes up the two layers (bilayer) of the cell membranes

• Composed of 3 basic parts:

o Charged phosphate group (the charged phosphate group and glycerol make up the polar, hydrophilic “head”)

o Glycerol

o Two fatty acid chains (non-polar, hydrophobic “tails”)

Fluid mosaic model

• The description term used for the cell membrane structure because it is flexible and, because the variety of proteins studding the membrane could be compared to an arrangement of tiles with different textures and patterns that make up a mosaic

Selective(semi) Permeability

• Allows some, but not all molecules to cross the phospholipid bilayer

• Enables cell to maintain homeostasis

• In general: small non-polar molecules easily pass through, small polar molecules transported through proteins, large molecules moved in vesicles

Receptors – 2 types

• Intracellular receptors are inside the cell and bind molecules that have crossed the cell membrane

• Membrane receptors bind to molecules that cannot enter the cell; when bound to a signal (ligand), the membrane receptor transmits the signal inside the cell by changing shape

Chapter 3.4

Passive transport

• Movement of molecules across a cell membrane without using energy – simple diffusion

Diffusion

• Movement of molecules in a fluid or gas from a region of high concentration to a region of lower concentration

• Results from random motion of particles

Concentration gradient

• The difference in the concentration of a substance from one location to another.

Osmosis

• The diffusion of water molecules across a semipermeable membrane from an area of high concentration of water to a lower concentration of water

Isotonic Solution

• Same concentration of solutes inside and outside a cell: water moves into and out of the cell at an equal rates, cell’s size stays constant

Hypertonic Solution

• Higher concentration of solutes outside the cell than inside the cell: more water exits the cell, causing the cell to shrivel or die

Hypotonic Solution

• Lower concentration of solutes outside the cell then inside the cell: more water enters the cell, causing the cell to expand or even burst

Facilitated diffusion

• Diffusion of molecules across a membrane using transport proteins

• Do not require energy by the cell

• Some transport proteins are simple channel, other proteins act like enzymes – changing shape, allowing a molecule to pass

Chapter 3.5

Active transport

• Drives a molecule across a membrane from low concentration to higher concentration using chemical energy (ATP)

• Transport proteins span the bilayer

• Most change shape when they bind to target molecule(s)

Endocytosis

• The process of taking liquids or large molecules into the cell by engulfing them in a membrane

Phagocytosis

• A type of endocytosis in which the cell membrane engulfs “eats” large particles.

Pinocytosis

• A type of endocytosis in which the cell membrane engulfs, “drinks” liquid with small molecules

Exocytosis

• The release of s substance out of the cell

• Vesicle with cellular material inside fuses with the cell membrane and releases the material

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