Cell Structure and Function

Unit 7

1 Robert Hookenamed cell while looking at cork in 1665

2 Anton van Leeuwenhoeksaw tiny organisms in pond

water in 1674

called them “animalcules”

3 The cell theory states:

• All living things are composed of cells. (1838 Schleiden said all plants; 1839 Schwann said all animals)

• Cells are the basic units of structure and function in living things.

• New cells are produced from existing cells. (1858, Rudolf Virchow)

4 Tools of the trade:Light vs. Electron

5 electron microscopes

• 1000 times better magnification than light microscopes

• must be placed in a vacuum • chemically preserve their samples first and then carefully

remove all of the water

– transmission electron microscopes (TEMs) • must be cut first into ultrathin slices so that you can see

what is inside

– scanning electron microscopes (SEMs)• produces stunning three-dimensional images• See the surface

7 Even though cells come in all shapes and sizes, what do all cells have?

DNACell Membrane

What are the levels of organization for a living thing?

Cell – Tissue – Organ – Organ System

In order to have different tissues and organs, cell must specialize for different functions.

• Carry out all 8 characteristics of living things, but…• No nucleus• Usually smaller and simpler• Usually unicellular organism• Example: bacteria

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9 prokaryotes - monerans

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• Have a nucleus• Contain several structures and internal

membranes• Can be unicellular (protists) or multicellular

organisms• Larger, more complex, and have a large

diversity (specialized)

11 Prokaryotes vs. Eukaryotes

12 Nucleus: the control center• Contains DNA that

contains the code to make proteins and other important molecules

• Has double-layer membrane with pores

• Has a nucleolus, which is a small dense region where ribosomes are made

13 Cytoplasm• Fluid-filled portion of the cell outside the

nucleus• Organelles are found here; literally means

“little organs”

14 Vacuoles: Storage

• Saclike membranes that store things like water, salts, proteins and carbohydrates

15 Specialized Vacuoles• In plants, have one central vacuole that stores

water that helps hold cell shape with water pressure

• Contractile vacuoles in some protists contract to expel water from the cell

16 Lysosomes: the clean-up crew• Small organelles filled with enzymes• Break down lipids, proteins and carbohydrates into

smaller molecules that the cell can use• Break down old organelles and other

unwanted/foreign material• All animals have these and some specialized plant cells

17 Cytoskeleton: structure• Helps the cell maintain shape and helps with

cell movement• Help with internal organization• Helps with transport within the cell, acting as

a conveyor belt

• The cytoskeleton is made up of microfilaments and microtubules

• Microfilaments: thin structures that help with support and cell movement (contract and relax for amoebic movement)

• Microtubules: important for cell shape and cell division

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19 Centrioles

• Microtubules found only in animal cells near the nucleus

• Help organize chromosomes on a network of microtubule fibers during cell division

20 Cilia and Flagella

• Microtubules found on the cell surface that help with movement

• Always in a 9 + 2 arrangement

21 Ribosomes: the machine!

• Where proteins are assembled• Made of RNA and protein• Found in the cytoplasm and attached the ER

22 Endoplasmic Reticulum (ER)• ER with ribosomes attached is called Rough ER• Rough ER - Modify proteins made by the ribosomes that

will be released/secreted from the cell or incorporated into the cell membrane

• Once the proteins are modified, they leave the ER by pinching off into a vesicle

• Found around the nucleus

Help transport materials in the cell

23 Smooth ER• Smooth ER (no ribosomes attached) is key in

creating cell membrane lipids and detoxifying (drugs)

24 Golgi Apparatus• Stack of flattened

membranes• Vesicles containing proteins

leave the ER and then merge with the Golgi Apparatus

• Here the proteins are modified, sorted and packaged either for storage in the cell or to be transported outside the cell

• They are then shipped out through another vesicle

25 Making a Protein

• DNA is encoded into mRNA in the nucleus• mRNA leaves the nucleus to go to the ribosomes• Ribosomes read the mRNA and create a protein

based on the code• Proteins enter the Rough ER for modification and

then are shipped via vesicles• Vesicles merge with Golgi Apparatus where they

are further modified and then packaged and shipped out through another vesicle

27 Chloroplasts

• Found in plants and other photosynthetic organisms

• Capture energy from the sun and convert it into a glucose (contains chemical energy): photosynthesis

• Two membranes• Contain stacks of membranes called granum• Contain chlorophyll – green pigment that

absorbs light

28 Chloroplasts

29 Mitochondria: the power plant• Found in nearly all eukaryotic cells• Convert chemical energy in glucose into

energy that the cell can use easier (ATP)• Have two membranes• Inner membrane is folded up inside the

organelle

30 Endosymbiotic Theory• Mitochondria and chloroplast both contain DNA• So, theory proposes that a symbiotic relationship between

primitive eukaryotic cells and the prokaryotic cells within them over time evolved into the eukaryotic cells we know today

31 Cell Wall• To support, shape and protect the cell; rigid• Lie outside the cell membrane• Porous to allow things like water, O2, and CO2 to pass easily• In plants (cellulose) and prokaryotes

32 Cell Membrane: traffic control• ALL cell have them!• Flexible lipid bilayer that regulates what enters

and leaves the cell, and also protects and supports

33 lipids in the cell membrane

• Hydrophobic tails are “protected” from water by forming a double layer with only the hydrophylic end coming in contact with water

34 Fluid Mosaic Model

• Various proteins are contained within the cell membrane, and many of these may have carbohydrate chains attached

• The variety creates a mosaic• These proteins are able to move freely among

the lipids in the lipid bilayer, making it appear to be a fluid

35 Fluid Mosaic

36 What do the proteins and carbohydrates do in the cell membrane?

• Proteins serve as channels and pumps to help move things in and out across the cell membrane

• Some proteins have a carbohydrate chain attached, and these serve to help cells recognize other cells like an identification card

37 Selectively Permeable

• Describes cell membranes because some things are allowed to enter and others are not

• Also called semi-permeable

38 Plant vs. Animal Cells

39 Cell Specialization

• We have seen the difference in prokaryotes and eukaryotes, and..

• We have seen the difference in plant and animal cells.

• The human body contains 210 different types of cells out of the approximate 100 trillion cells in your body!

• These cells vary in shape, size, and the amount of organelles that they contain, all dependent upon the cell’s function

40 Different Human Cells