Chapter 3: The Cell

Cell

• is the fundamental unit of life

• many cells interact to form tissues, organs, and organ systems

• differences in cell shape make different functions possible

• genes control a cell’s actions and responses 

Composite cell

• includes many different cell structures at once

• most cells contain most of these structures

• used to describe the functions and organelles of cells

What are the three main parts of a cell ?

Nucleus, Cytoplasm, & Cell membrane

Nucleus

Contains DNA (genetic material) and directs cell’s activities 

Cytoplasm

organelles and fluids that make up the majority of the cell; between nucleus and cell membrane

Cell membrane

boundary that encloses the cell

What is within the cytoplasm that is specialized and performs functions for the cell ?

Organelles 

Cytosol

organelles that are suspended in a fluid

Cell membrane ( plasma membrane )

is a very thin boundary that contains the cell’s contents 

The cell membrane is Selectively Permeable

regulates the movement of substances in and out of the cell

• helps cells adhere to other cells

What is the cell membrane composed of ?

Mainly of lipids and proteins, and some carbohydrates

Double layer (bilayer) of phospholipids

• the basic framework of the cell membrane consists of a double layer (bilayer) of phospholipids, with fatty acids tails turn inward and the water-soluble heads facing the surfaces 

• the phospholipids can move, forming a stable fluid film

Many types of _____ are found in the cell membrane.

proteins

Some proteins function as _____ on the cell surface

receptors

Other proteins transport ions or molecules across cell membrane, such as _______

ion channels

Other proteins are used for ______________; this helps identify cells as “self”, protecting them from attack by the immune system

cell identification 

• some proteins will protrude into the cell will anchor supportive rods and tubules, forming a cytoskeleton

What makes most of the cell volume ?

cytoplasm

The Cytoplasm consist of ?

• a clear liquid (cytosol)

• a supportive cytoskeleton

• networks of membranes and organelles

Ribosomes

• tiny structures composed of RNA and protein

• produce proteins for the cell

• not membranous 

• found in cytoplasm or bound to rough endoplasmic reticulum 

Endoplasmic reticulum (ER)

• made up of membranes, flattened sacs, and vesicles

• provides a tubular transport system inside the cell

• functions as a transport network throughout the cell

Rough ER

contains ribosomes and functions in protein synthesis and processing

Smooth ER

does not contain ribosomes and functions in lipid synthesis, absorption of fats, and metabolism of drugs

Vesicles

• membranous sacs

• store or transport substances within or between cells

Golgi apparatus

• composed of flattened, membranous sacs

• refines, packages, and transports proteins formed in the rough ER

• vesicles formed in the ER travel to the Golgi apparatus, which may modify their contents by adding sugar molecules to the proteins, to stabilize their structure or to enable folding

• a new vesicle pinches off the Golgi apparatus and may then move to the cel membrane to secrete its contents to the outside (exocytosis)

Vesicular Movement

• vesicles formed in the ER travel to the Golgi apparatus, which may modify their contents buy adding sugar molecules to the proteins, to stabilize their structure or to enable folding

• a new vesicle pinches off the Golgi apparatus and may then move to the cell membrane to secrete its contents to the outside (exocytosis)

Mitochondria (ATP)

• elongated fluid-filled sacs

• house many chemical reactions that extract energy from nutrients

• contain enzymes needed for cellular respiration

• the inner membrane of the mitochondrion is folded into cristae, which hold the enzymes needed in energy transformations to make ATP

• store the energy in chemical bonds of ATP

• very active cells contain thousands of mitochondria

• mitochondria have their own DNA and reproduce by dividing

Lysosomes

• membranous sacs

• contain enzymes that break down nutrients, ingested, materials, debris, worn out cell parts, cholesterol (in some cells), toxins, and drugs 

Peroxisomes

• also membranous sacs

• contain a different set of enzymes than lysosomes

• their enzymes function in the breakdown of fatty acids and hydrogen peroxide, and detoxification of alcohol 

In the cytoplasm, there are several structures, which are not organelles, but rather part of the ________.

cytoskeleton

_________ and _________ are thin, threadlike structures that serve as the cytoskeleton of the cell.

Microfilaments and microtubules