A Tour of the Cell Lecture 6

The Cell Theory States that

all living things are composed of cells and that all cells come from earlier cells

Organisms are either

single-celled, such as most prokaryotes and protists, or multi-celled, such as plants, animals, and most fungi

The countless cells that exist on Earth can be placed into two basic categories:

Prokaryotic or Eukaryotic

Eukaryotic cells

(found in organisms of the domain Eukarya — including protists, plants, fungi, and animals — are composed of eukaryotic cells and are called eukaryotes)

Eukaryotic

cells (found in organisms of the domains Bacteria and Archaea, known as prokaryotes)

Prokaryotic and Eukaryotic cells have several features

in common: They are all bounded

by a barrier called a plasma membrane, which regulates the traffic of molecules between the cell and its surroundings

Inside all cells is a thick, jellylike fluid called the

cytosol, in which cellular components are suspended

All cells have one or more

chromosomes carrying genes made of DNA

All cells have

ribosomes that build proteins according to instructions from the genes

Prokaryotic and Eukaryotic cells differ in several important ways:

– Fossil evidence shows that

prokaryotes were the first life on Earth, appearing more than 3.5 billion years ago, while the first eukaryotes did not appear until around 2.1 billion years ago

Prokaryotic cells are usually much

smaller and less complex than eukaryotic cells

The most significant structural difference between the two types of cells is that

eukaryotic cells have organelles (“little organs”) – membrane-enclosed structures that perform specific functions, and prokaryotic cells do not

The plasma membrane is the boundary that separates the

living cell from its nonliving surroundings

It is a remarkable thin film that can regulate the traffic of chemicals

into and out of the cell

Plasma Membrane is Composed mostly of

phospholipids

phospholipids: has two distinct regions

a “head” with a negatively charged phosphate group and two nonpolar fatty acid “tails”

phospholipids: group together to form a

two-layer sheet called a phospholipid bilayer

phospholipids: phospholipid bilayer contains

proteins that help regulate traffic across the membrane

The phospholipids and most of the proteins can drift about within the

membrane

a membrane is a

fluid mosaic: fluid because the molecules can move freely past one another and mosaic because of the diversity of proteins that float like icebergs in the phospholipid sea

Unlike plant cells, animal cells lack

a cell wall

most

animal cells secrete a sticky coat called the

extracellular matrix (ECM)

extracellular matrix (ECM)

Fibers made of the protein collagen hold cells together in tissues and can also have protective and supportive functions

the surfaces of most animal cells contain

cell junctions

cell junctions are

Structures that connect cells together into tissues, allowing the cells to function in a coordinated way

The nucleus is separated from the cytoplasm by a double membrane called the

nuclear envelope

Pores in the envelope allow certain materials to pass between

the nucleus and the surrounding cytoplasm

Within the nucleus, long DNA molecules and associated proteins form fibers called

chromatin

Each long chromatin fiber constitutes

one chromosome

The number of chromosomes in a cell depends on

the species

each human body cell has

46 chromosomes

The ___ is a prominent structure within the nucleus, and is the site where the components of ribosomes are made

nucleolus

Ribosomes are responsible for

protein synthesis

Some ribosomes are suspended in the

cytosol, making proteins that remain within the fluid of the cell

Other ribosomes are attached to the outside of the nucleus or an organelle called the

endoplasmic reticulum, making proteins that are incorporated into membranes or secreted by the cell

Free and bound ribosomes are structurally identical, and ribosomes can switch locations, moving between the

endoplasmic reticulum and the cytosol

Cells that make a lot of proteins have a

large number of ribosomes

DNA transfers its coded information to a molecule called

messenger RNA (mRNA)

The mRNA molecule carries the order to

“build this type of protein”

The mRNA exits the nucleus through pores in the nuclear envelope and travels to the

cytoplasm, where it binds to a ribosome

The ribosome moves along the mRNA, translating the genetic message into a

protein with a specific amino acid sequence

The cytoplasm of a eukaryotic cell is filled with organelles that form the

endomembrane system

endomembrane system

1. nuclear envelope

2. endoplasmic reticulum

3. Golgi apparatus

4. Lysosomes

5. vacuoles

One of the main manufacturing facilities within a cell

Endoplasmic Reticulum (ER)

Two components make up the ER:

1. Rough ER

2. Smooth ER

Rough ER:

refers to ribosomes that stud the outside of its membrane. One of the functions of rough ER is to make more membrane. The ribosomes attached to the rough ER produce proteins

Smooth ER

have no ribosomes attached. A diversity of enzymes built into the smooth ER membrane enables this organelle to perform many functions. One is the synthesis of lipids, including steroids

Rough ER manufactures and packages

secretory proteins

The Golgi Apparatus funtion

Receives, refines, stores, and distributes chemical products of the cell

The Golgi apparatus receives

proteins from the ER via transport vesicles, processes the proteins, and then dispatches them in vesicles

Proteins are usually modified by

enzymes during their transit in the Golgi apparatus

Products can be carried in

transport vesicles to other organelles or to the plasma membrane from the Golgi apparatus

Lysosomes are membrane-enclosed sac of

digestive enzymes found in animal cells

Lysosomes develop from vesicles that

bud off from the Golgi apparatus

Enzymes within a lysosome can

break down large molecules such as proteins, polysaccharides, fats, and nucleic acids

Lysosomes also help

destroy harmful bacteria. For example, your white blood cells ingest bacteria into vacuoles, and lysosomal enzymes that are emptied into these vacuoles rupture the bacterial cell walls

Vacuoles large sacs made of

membrane that bud off from the ER or Golgi apparatus

Vacuoles have a variety of functions:

1. food vacuole – buds from the plasma membrane

2. contractile vacuoles – pump out excess water that flows into protist cells

Chloroplasts are unique to the photosynthetic cells of

plants and algae

Chloroplasts are the organelles that perform

photosynthesis

photosynthesis:

the conversion of light energy from the sun to the chemical energy of sugar and other organic molecules

Mitochondria are found in almost all

eukaryotic cells, including those of plants and animals

Mitochondria are the organelles in which

cellular respiration takes place; during cellular respiration, energy is harvested from sugars and transformed into another form of chemical energy called ATP (adenosine triphosphate)

Mitochondria Cells use

molecules of ATP as a direct energy source

Mitochondria contain their own

DNA that encodes some of their own proteins made by their own ribosomes

An envelope of two membranes encloses the mitochondrion. The

inner membrane of the envelope has numerous infoldings called

cristae

the cristae create a

Large surface area in which many of the enzymes and other molecules that function in cellular respiration are embedded, thereby maximizing ATP output

The Cytoskeleton is a Network of protein fibers

extending throughout the cytoplasm

The Cytoskeleton Serves as both

skeleton and “muscles” for the cell, functioning in support and movement

The Cytoskeleton Gives

mechanical support to the cell and maintain its shape

The Cytoskeleton Contains several types of

fibers made from different types of protein

The Cytoskeleton Contains several types of fibers made from different types of protein

– Microtubules

hollow tubes of protein

The Cytoskeleton: Contains several types of fibers made from different types of protein

– Cytoskeletal fibers, called

intermediate filaments and microfilaments, are thinner and solid

Without the cytoskeleton, your cells would

collapse in on themselves, much like a house collapses when the infrastructure fails

The cytoskeleton provides

anchorage and reinforcement for many organelles in a cell:

he nucleus is held in place by a

“cage” of cytoskeletal filaments

Other organelles use the cytoskeleton for

movement

a lysosome might reach a

food vacuole by gliding along a microtubule track

Microtubules also guide the

movement of chromosomes when cells divide

In some eukaryotic cells, microtubules are arranged into structures called

flagella and cilia, extensions from a cell that aid in movement

Eukaryotic flagella propel cells with an

undulating, whip-like motion

Often occur singly, such as in human sperm cells but may also appear in groups on the outer surface

Cilia are generally

shorter and more numerous than flagella and move in a coordinated back-and- forth motion, like the rhythmic oars of a crew team

Both cilia and flagella propel

various protists through water

Cilia and flagella have the

same basic architecture

You look into a microscope and view an unknown cell. What might you see that would tell you whether the cell is prokaryotic or eukaryotic?

Explain how each word in the term fluid mosaic describes the structure of a membrane.

A membrane is fluid because its components are not locked into place. A membrane is mosaic because it contains a variety of suspended proteins

Identify which of the following structures includes all the others in the list: rough ER, smooth ER, endomembrane system, the Golgi apparatus

The ER has two distinct regions that differ in structure and function. Lipids are synthesized within the _________, and proteins are synthesized within the _________.

A type of cell called a lymphocyte makes proteins that are exported from the cell. You can track the path of these proteins within the cell from production through export by labeling them with radioactive isotopes. Identify which of the following structures would be radioactively labeled in your experiment, listing them in the order in which they would be labeled:

chloroplasts, Golgi apparatus, plasma membrane, smooth ER, rough ER, nucleus, mitochondria.

Name two similarities in the structure or function of chloroplasts and mitochondria. Name two differences.

Both organelles use membranes to organize enzymes and both provide energy to the cell

a. ribosomes

b. microtubules

c. mitochondria

3. protein synthesis

d. chloroplasts

2. photosynthesis

e. lysosomes

DNA controls the cell by transmitting genetic messages that result in protein production. Place the following organelles in the order that represents the flow of genetic information from the DNA through the cell:

Compare and contrast cilia and flagella.

Both are appendages that aid in movement and that extend from the surface of a cell. Cells with flagella typically have one long flagellum that propels the cell in a whip-like motion; cilia are usually shorter, are more numerous, and beat in a coordinated fashion.