cells

Units of life

The cell is a unit of organization

Cell vocabulary

• 1. cell• 2. plasma membrane• 3. organelles• 4. surface area• 5. membrane• 6. nucleus• 7. nucleolus• 8. mitochondria • 9. ribosomes• 10. cytoplasm• 11. endoplasmic reticulum• 12. chloroplasts• 13. prokaryotic cells• 14. eukaryotic cells

History of studying cells

• Because of the limitations of the human eye, much of the early biological research concentrated on developing tools to help us see very small things.

• As imaging technology became more sophisticated, biological discoveries abounded.

• Next is a timeline detailing some of those major events in biology.

• What are the respective sizes of a virus and a plant cell?

• A.3 mm, 30 mm

• B.30 nm, 30 µm

• C.30 µm, 30 nm

• D.3 cm, 30 cm

B.30 nm, 30 µm

The Cell Theory • When Schleiden and Schwann proposed the

cell theory in 1838, cell biology research was forever changed. The cell theory states that:

Cell theory

• All life forms are made from one or more cells.

• Cells only arise from pre-existing cells.

• The cell is the smallest form of life.

• The cell theory also provides us with an operational definition of "life".

• Which of the following is not a part of the cell theory?

• A.All animals are formed by cells.

• B.Reproduction requires vegetative duplication or the sexual mixing of gametes.

• C.Cells are the smallest form of life.

• D.Abnormal cells self destruct by apoptosis.

• D. Abnormal cells self destruct by apoptosis

• Living things are classified in six kingdoms based on structure.

• Monera (Eubacteria) Prokaryotic

• Archaea Prokaryotic

• Protista Eukaryotic

• Plantae Eukaryotic

• Fungae Eukaryotic

• Animalia Eukaryotic

Within prokaryotes

• which appeared 3.5 billion years ago, are the kingdoms

• Monera (Eubacteria) and Archaea.

Within eukaryotes

• which evolved 1.5 billion years ago, are the kingdoms

• Protista, Plantae, Fungae, Animalia.

• Cells are also defined according the need for energy.

Autotrophs

• are "self feeders" that use light or chemical energy to make food. Plants are an example of autotrophs.

heterotrophs

• In contrast, heterotrophs ("other feeders") obtain energy from other autotrophs or heterotrophs. Many bacteria and animals are heterotrophs.

Multicellular Organisms

• Multicellular organisms are created from a complex organization of cooperating cells.

• There must be new mechanisms for cell to cell communication and regulation.

• There also must be unique mechanisms for a single fertilized egg to develop into all the different kinds of tissues of the body.

• In humans, there are 1014 cells comprising 200 kinds of tissues!

• Cells are classified by fundamental units of structure and by the way they obtain energy.

• Cells are classified as prokaryotes or eukaryotes

Prokaryotes

• prokaryotes include the kingdoms of Monera (simple bacteria) and Archaea.

• Simply stated, prokaryotes are molecules surrounded by a membrane and cell wall.

•

• Prokaryotic cells lack characteristic eukaryotic sub cellular membrane enclosed "organelles", but may contain membrane systems inside a cell wall.

Bacteria & antibiotics

• The cell wall is the target for antibiotics, as well as for carbohydrates that our immune system uses to detect infection. A major threat to humankind is the antibiotic-resistant strains of bacteria have been selected by overuse of antibiotics.

If you were bacteria • You have 0.001 times as much DNA as a

eukaryotic cell. • You live in a medium which has a viscosity about

equal to asphalt.

• You have a wonderful "motor" for swimming. Unfortunately, your motor can only run in two directions and at one speed. In forward, you are propelled in one direction at 30 mph. In reverse your motor makes you turn flips or tumble. You can only do one or the other. You cannot stop.

• While you can "learn", you divide every twenty minutes and have to restart your education.

• You can have sex, with males possessing a sexual apparatus for transferring genetic information to receptive females. However, since you are both going 30 mph it is difficult to find each other.

• Furthermore, if you are male, nature gave you a severe problem. Every time you mate with a female, she turns into a male. In bacteria, "maleness" is an infective venereal disease.

• Also, at fairly high frequencies, spontaneous mutations cause you to turn into a female.

• Eukaryotes have enslaved some of your "brethren" to use as energy generating mitochondria and chloroplasts.

• They are also using you as a tool in a massive effort to understand genetics. The method of recombinant DNA is designed to exploit you for their own good.

• The last laugh may be yours. You have spent three and a half billion years practicing chemical warfare. Humans thought that antibiotics would end infectious diseases, but the overuse of drugs has resulted in the selection of drug resistant bacteria. They didn't realize that this was only the first battle, and now the war is ready to begin.

• Humans think this is their era. A more truthful statement would be that we all live in the age of bacteria.

• Eukaryotes • Basic structure The basic eukaryotic cell

contains the following: • plasma membrane • glycocalyx (components external to the

plasma membrane) • cytoplasm (semi fluid) • cytoskeleton - microfilaments and

microtubules that suspend organelles, give shape, and allow motion

• presence of characteristic membrane enclosed subcellular organelles

organelles

• Plasma Membrane

• A lipid/protein/carbohydrate complex, providing a barrier and containing transport and signaling systems.

Nucleus• Double membrane surrounding the

chromosomes and the nucleolus. Pores allow specific communication with the cytoplasm. The nucleolus is a site for synthesis of RNA making up the ribosome

• Mitochondria

• Surrounded by a double membrane with a series of folds called cristae. Functions in energy production through metabolism. Contains its own DNA, and is believed to have originated as a captured bacterium.

•

Chloroplasts (plastids)• Surrounded by a double membrane, containing

stacked thylacoid membranes. Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars. Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.

•

Rough endoplasmic reticulum (RER)

• A network of interconnected membranes forming channels within the cell. Covered with ribosomes (causing the "rough" appearance) which are in the process of synthesizing proteins for secretion or localization in membranes.

• Smooth endoplasmic reticulum (SER)

• A network of interconnected membranes forming channels within the cell. A site for synthesis and metabolism of lipids. Also contains enzymes for detoxifying chemicals including drugs and pesticides.

•

Golgi apparatus• A series of stacked membranes. Vesicles

(small membrane surrounded bags) carry materials from the RER to the Golgi apparatus. Vesicles move between the stacks while the proteins are "processed" to a mature form. Vesicles then carry newly formed membrane and secreted proteins to their final destinations including secretion or membrane localization.

Ribosomes• Protein and RNA complex responsible for

protein synthesis.

• VacuolesMembrane surrounded "bags" that contain water and storage materials in plants.

Cell wall

• Plants have a rigid cell wall in addition to their cell membranes.

Peroxisomes or Microbodies

•Produce and degrade hydrogen peroxide, a toxic compound that can be produced during metabolism

Lysosymes

• A membrane bound organelle that is responsible for degrading proteins and membranes in the cell, and also helps degrade materials ingested by the cell.

Cell membrane plasma

membrane

• The cell membrane is the thin nearly invisible structure that surrounds the cytoplasm of the cell.

• In this section we will talk about its structure and its function.

• In the image you can see that it is a continuous membrane that completely surrounds the cell.

Floating around in the cell membrane are different kinds of proteins. These are generally globular proteins. They are not held in any fixed pattern but instead float around in the phospholipid layer.

There are carrier proteins that regulate transport and diffusion

Cell membrane - Function • The cell membrane's function, in general,

revolves around is membrane proteins. General functions include:

• Receptor proteins which allow cells to communicate,

• transport proteins regulate what enters or leaves the cell,

• and marker proteins which identify the cell

Cell membrane - Function - Regulation of transport

• Transport Proteins come in two forms: Carrier proteins are peripheral proteins which do not extend all the way through the membrane. They move specific molecules through the membrane one at a time.

Channel proteins extend through the bilipid layer. They form a pore through the membrane that can

move molecules in several ways.

Cell membrane - Function - Carrier Proteins

• These are carrier proteins. They do not extend through the membrane. They bond and drag molecules through the bilipid layer and release them on the opposite side.

Symports also use the process of diffusion. In this case a molecule that is moving naturally into the cell through

diffusion is used to drag another molecule into the cell. In this

example glucose hitches a ride with sodium.

• The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins.

• This process is known as endocytosis.

• In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell.

• In this animation an ameba engulfs a food particle.

Endocytosis

Exocytosis

• The opposite of endocytosis is exocytosis.

• Large molecules that are manufactured in the cell are released through the cell membrane.

Proteins in the membrane• There are carrier proteins that

regulate transport and diffusion

• Marker proteins that identify the cell to other cells

• And receptor proteins that allow the cell to receive instructions

NUCLEUS

• The nucleus is the headquarters of the cell.

• It regulates all cell activity.

• It consists of a nuclear envelope, (the outer membrane) and nucleoplasm.

• In the nucleoplasm you can see chromatin and the nucleolus.

• The nuclear envelope is a double membrane. Is has 4 phospholipid layers. It is also has large pores through which materials pass back and forth.

• Within the nucleus are found chromatin and a structure called the nucleolus.

• Chromatin is DNA in its active form. It consists of DNA looped around histone proteins.

• The nucleolus is a knot of chromatin.

• It is the nucleolus that manufactures ribosomes

Nucleus - Function • The nucleus regulates all cell activity.

• It does this by controlling the enzymes present.

• The chromatin is composed of DNA.

• DNA contains the information for the production of proteins.

• This information is encoded in the 4 DNA bases.

• Adenine, thymine, cytocine, and guanine.

• The specific sequence of these bases tells the cell what order to put the amino acids.

• There are three processes that enable the cell to manufacture protein:

• Replication allows the nucleus to make exact copies of its DNA

•Transcription allows the cell to make RNA working copies of its DNA

• In translation the Messenger RNA is used to line up amino acids into a protein molecule

Cytoplasm

• The term cytoplasm refers to everything between the cell membrane and the nuclear envelope. It consists of primarily of water. It also contains various organelles as well as salts, dissolved gasses and nutrients.

Those organelles involved in protein production

• Ribosomes

• The endoplastic reticulum

• The golgi apparatus

• Lysosomes

Those organelles involved in energy production

• Mitochondria

• Chloroplasts

Specialty organelles • these structures are usually found only in certain kinds

of cells.

Animal cells generally contain centrioles.

• Plant cells generally contain storage vacuoles, cell walls, and plastids.

• Cilia and flagella are found in many different life forms.

Be aware that there are many other kinds of living things besides plants and animals.

Centrioles

• Centrioles are found only in animal cells. They function in cell division. Notice the 9 sets of 3 arrangement of the protein fibers

Vacuoles • Vacuoles are large empty appearing areas

found in the cytoplasm.

• They are usually found in plant cells where they store waste.

• As a plant cell ages they get larger.

• In mature cells they occupy most of the cytoplasm.

Cell Wall

• Cell walls are the rigid structure found surrounding plant cells. They provide support for the plant

Plastids

• Plastids are large organelles found on plants and some protists but not in animals or fungi. They can easily be seen through a light microscope. Chloroplasts represent one group of plastids called chromoplasts (colored plastids). The other plastids are called leucoplasts (colorless plastids); they usually store food molecules. Included in this group are amyloplasts or starch plastids shown here in potato root cell.

Cillia and Flagella

• These are hair like extensions off of the cell membrane. Their structures are similar except that cillia tend to be small and numerous and flagella tent to be large and fewer. Their they beat back and forth rhythmically. In unicellular organisms their job is locomotion. In large multicellular organisms their role is to move fluid past the cell. Notice the 9+2 arrangement of the microtubules

Contractile Vacuoles

• These organelles are critical in enabling protozoa to combat the effects of osmosis. Protozoa must constantly excrete the water that enters through their membranes.

The Chloroplast

• The Chloroplast is the photosynthesis. It is here that plant cells trap the energy of light and use it to manufacture food proteins for the cell.

The Mitochondrion

• The mitochondrion is the site of aerobic respiration. Most of the key processes of aerobic respiration occur across its inner membrane. One theory holds that they evolved from endosymbiotic bacteria.

The Endoplastic Reticulum

• Spreading throughout the cytoplasm is the endoplasmic reticulum. It is a folded system of membranes that loop back and forth giving it a very large surface area. This membrane provides a surface area for cell reactions. It is also the Site of lipid production.

• Smooth E.R. has no ribosomes associated with it  The rough E.R. has ribosomes

Ribosome

• The rough E.R. has ribosomes attached to it. This gives it its texture. These ribosomes manufacture proteins for the cell.

The Golgi Apparatus

• The golgi body is responsible for packaging proteins for the cell. Once the proteins are produced by the rough E.R. they pass into the sack like cisternae that are the main part of the golgi body. These proteins are then squeezed off into the little blebs which drift off into the cytoplasm.

Lysosomes

• Lysosomes are called suicide sacks. They are produced by the golgi body. They consist of a single membrane surrounding powerful digestive enzymes.

Cell characteristics • Size:

• 1. smallest cells are bacteria a. 0.2 um in diameter

• 2. longest cells in mammals

a. nerve cells, giraffe neck

Typical sizes

• 1. bacteria (prokaryotes)

a. diameter 1-5 um

• 2. higher plant & animal cells (eukaryotes) a. 10-50 um

• 3. eukaryotic cells are about 1000x larger in volume than prokaryotic cells

surface area

Why are cells these sizes?

• surface area/volume ratio (SA/V) everything entering cell comes

through the plasma membrane (PM)

An increased cytoplasmic volume means more stuff must come thru

-more glucose -more amino acids -more ions -more of everything needed in the cell

Surface area to volume ratio

Bigger cell means

An increased volume => relative decline in Surface area to volume ratio

Plasma Membrane loses ability to transport enough stuff in/out of cell

Solutions to the surface Area Problem

• (1) infoldings (increases SA) • (2) outward protrusions (increases SA) • note the projections that increase surface

area w/o increasing volume much

• e.g.: microvilli of • intestinal mucosa • cells

Other solutions

large vacuoles => decreases cytoplasm volume

(a) Elodea cell

with vacuole

indicated

membrane

nucleus

nucleolus

ribosomes

cytoplasm

• Microfilaments and microfibrils

endoplasmic reticulum

chloroplasts

mitochondria

prokaryotic cells

eukaryotic cells

• Plant, animal, fungal and Protista cells

Giant Plant Cell

– nucleus and nucleolus – mitochondrion – chloroplast – rough endoplasmic reticulum (focus on function of ribosome) – smooth endoplasmic reticulum (focus on function of ER) – Golgi complex – lysosomes – peroxisomes – microtubules and microfilaments – vacuole

• _ cytoskeleton

• 1. Students research the structure and function of their chosen organelle.

• 2. Students produce a blueprint describing how they will construct their model and its size.

• 3. Students prepare a class presentation.

Organelle Nucleus

Function1. stores the cell's

hereditary material, or DNA

2. coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).

Structure

Nucleolus manufacture the subunits that combine to form ribosomes

Organelle

Plasma Membrane

Function

acts as a boundary, holding the cell together and keeping other substances from entering.

Structure

OrganelleMicrofilament

Function

These filaments are primarily structural in function and are an important component of the cytoskeleton.

structure Microfilaments are solid rods made of globular proteins

Microtubules  are found throughout the cytoplasm of all eukaryotic cells (prokaryotes don't have them) and carry out functions, ranging from transport to structural support.

straight, hollow cylinders

Organelle function Structure

Cell Wall

 

protects intracellular contents, provides rigidity, is a porous medium for the circulation and distribution of water, minerals, and other nutrients, and houses specialized molecules that regulate growth and protect the plant from disease.

Organelle function Structure

Mitochondrion  break down carbohydrate and sugar molecules to provide energy

oblong shaped organelles

OrganelleChloroplast

Function

contains the pigment chlorophyll. It absorbs light energy needed for photosynthesis to occur.

Structure

Organelle Endoplasmic Reticulum

Function

manufactures, processes, and transports chemical compounds for use inside and outside of the cell.

It is connected to the double-layered nuclear envelope, providing a pipeline between the nucleus and the cytoplasm.

structure

network of sacs

Organelle Ribosome

Function

serve as the protein production machinery for the cell

structure composed of approximately 60 percent RNA and 40 percent

protein.

Vacuole

50-80% of volume

plant cells have a large, single vacuole that stores things, helps in plant growth, and plays an important structural role for the plant.

Organelle function StructurePeroxisomes  spherical and bound

by a single membrane. There are several types of microbodies but peroxisomes are the most common.

CILLIA/ Flagella locomotion of organisms. In multicellular organisms, cilia function to move fluid or materials past an immobile cell as well as moving

a cell or group of cells.

• Creating the Organelles

• The Giant Plant Cell is shaped like a giant cube that is 3 meters (300 cm) on each edge. You have been provided with a chart of actual cell organelle sizes.

• You must, using ratios, calculate the size of your giant organelle so that it is proportionately correct for the huge cell.

• You also need to research the function of the organelle in order to build it so that it can carry out its role in the giant cell.

• First, you will prepare an architectural design plan that will be evaluated by your teacher.

• Then you will build your organelle.

• You will prepare a 3-5 minute report to present to the class.

• Your organelle will be judged according to the accuracy of its size, the correctness of its details, your explanation of its function

Equation for determining size of organelle:

• Size of giant organelle =Actual size of organelle

• Size of giant cell (300 cm) =Actual size of average plant cell (30mm)

Basic Requirements• Construction of Organelle

– All constructed organelles must be 3-dimensional. – All organelles must show internal and external details. – All organelles must be the correct size for the colossal plant

cell.• Oral Presentation

– Reports should be about 3-5 minutes long. – Each member of the team should do part of the

presentation. – The presentation should include details about the organelle's

structure and function. – The presentation should include a discussion about how

many of the organelles will be manufactured for the colossal plant cell.

– The presentation should also include an explanation of the actual and giant size of the organelle.

• CHART OF ACTUAL ORGANELLE SIZES

• Cell or Organelle Size in x (10-3 mm 

Average Plant Cell  30 x 

Nucleus  7.5-10 x

Nucleolus  2.5 x

Plasma Membrane  0.009 x thick

Mitochondrion  0.2-1 x wide x 3-10 x long

Chloroplast (other plastids are similar sizes) 2 x 5 x

Ribosome  0.025 x

Endoplasmic Reticulum (in most plant cells) 0.5 x thick (2 membranes of 0.009 mm with 0.03 mm compartment between them) 

Golgi Complex 1 x 1 x (membranes have thickness of ER)

Vacuole (central) sometimes serves as lysosome 50-80% of volume of cell

Microtubules  0.02 x diameter

Microfilaments  0.007 0.5-1 x diameter

Lysosomes (in some plant cells)  0.2-2 x

Peroxisomes  3 x

Cell Wall  1-2 x thick

Questions• How is a typical plant cell the same as a prokaryotic cell? How is a typical plant cell

different from a prokaryotic cell?• How are plant and animal cells similar? How are plant and animal cells different?• Discuss the interaction of the mitochondria and the chloroplasts. What substances do

each produce that the other uses?• Given the size of the organelles, which structures would you expect to see with a

typical light microscope (magnifies 400x)? Explain your reasoning.• How would a plant cell found in the petal of a flower be different from/similar to a

"typical plant cell" such as the Giant Plant Cell?• If the giant plant cell was a leaf cell, describe what you would need to add to the cell

to help it function.• Describe how proteins are synthesized in a plant cell.• How is the cellular structure of terrestrial plants different from that of aquatic plants?• If you were looking at a root cell, a leaf cell, and a stem cell what differences would

you find?• How is carbon cycled in a plant? In a plant cell?• What happens to the molecules that are formed by the chloroplasts?• What happens to the molecules that are formed by the mitochondria?