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Chapter 3 – Cell Structure & FunctionHistory of the cell
Antonie van Leeuwenhoek (1673) – constructed a crude microscope to analyze “animalcules” in pond water & other “tiny things”
Robert Hooke (1665) – coined the word “cellulae” (small roon) to describe the boxlike cavities he saw when viewing cork slices under a microscope
Both of these individuals observations were discarded for nearly 200 years, due to social standing
Development of the CELL THEORY
Matthias Schleiden (1838) – using a microscope proposed that all plants are composed of cells
Theodor Schwann (1839) – using a microscope proposed that all animals are composed of cells
Together they stated:
1. Cells are the elementary particle of all living organisms
2. All cells are alive – independent to the organisms to which they belong
Chapter 3 – Cell Structure & FunctionDevelopment of the CELL THEORY
Rudolf Virchow (1858) – stated
1. Cells never arise from noncellular material
2. Diseases result from changes in specific kinds of cells
CELL THEORY
1. All organisms are composed of one or more cells
2. Cells are the basic living unit of organization of all organisms capable of independent existence
3. All cells come from other cells
Chapter 3 – Cell Structure & FunctionCell size
Chapter 3 – Cell Structure & FunctionWhy are cells so small?
Surface area / Volume ratio
Nutrients & wastes enter & exit a cell via its surface (plasma membrane)
Do you think a larger cell needs more nutrients & produces more wastes than a smaller cell?
The only problem here is that as a cell gets larger, the proportionate amount of surface area actually decreases
That is the amount of surface area as a ratio to the volume decreases, meaning that a larger cell cannot bring in enough nutrients or expel enough wastes even though its overall surface area is quite large
EXAMPLE
1 mm cube has a surface area of 6 mm2 and a volume of 1 mm3 = 6:1 SA to V ratio
2 mm cube has a surface area of 24 mm2, but a volume of 8 mm3 = 3:1 SA to V ratio
A cell needs a surface area that can adequately exchange materials with the environment. Surface area to volume considerations require that cells stay small
Chapter 3 – Cell Structure & FunctionWhat are cells composed of?
All cells are composed of a boundary, a cell body, & a set of genes
The plasma membrane is a boundary that separates the contents of the cell from the surrounding environment
It is composed of a phospholipid bilayer in which protein molecules are embedded
It serves to regulate the passage of materials into & out of the cell, thus maintaining a homeostatic environment for the cell’ life processes
Chapter 3 – Cell Structure & FunctionCells also contain a set of genes, which are composed of DNA
Genes contain all of the necessary information for the growth, development, & maintenance of an organism throughout its life cycle
In our cells, along with those of plants, fungi (mushrooms), & protists (amoeba), the genes are contained within a membrane bound structure called a nucleus. The presence of this nucleus defines a category of cells called eukaryotic cells
Prokaryotic cells (bacteria) do not possess a gene containing nucleus. Its genes occupy a region called the nucleoid. It is not protected by a membrane barrier.
The cell body is defined as the area between the nucleus & the plasma membrane
It is filled with a semi-fluid substance called cytoplasm
Cytoplasm is 90% water & contains dissolved molecules as well as the organelles of the cell
Chapter 3 – Cell Structure & Function
Chapter 3 – Cell Structure & FunctionWhat kind of functions does a cell have to accomplish in order to survive?
Organelles & their functions
Nucleus – Stores genetic information for the cell. It is surrounded by a double membrane called the nuclear envelope.
The nuclear envelope contains nuclear pores to allow the passage of materials between the nucleus & the cytoplasm
The nucleus also contains nucleoli which synthesizeribosomes necessary for protein synthesis
Chapter 3 – Cell Structure & Function
Chapter 3 – Cell Structure & FunctionThe endomembrane system – is composed of the nuclear envelope, endoplasmic reticulum, golgi apparatus, & vesicles
Endoplasmic reticulum (ER) – a series of flattened stacks of vesicles (saccules) which are continuous with the outer membrane of the nuclear envelope
ER exists as either Smooth ER (SER) or Rough ER (RER)
RER is studded with ribosomes, giving the ER its “rough”appearance. It is involved in protein synthesis, packaging the newly synthesized proteins for further modification
SER does not have attached ribosomes, hence smooth appearance. It is involved in lipid metabolism, hormone production, detoxification, vesicle formation, & other processes
Chapter 3 – Cell Structure & Function
Chapter 3 – Cell Structure & Function
Chapter 3 – Cell Structure & FunctionGolgi apparatus – a stack of 3 to 20 saccules which are involved in modifying & packaging proteins & lipids delivered to it from the ER
Once the molecules have been modified, they exit the Golgi via vesicles which will then migrate to the plasma membrane to secrete the molecule or have them embeddedin the plasma membrane
Other vesicles will remain in the cytoplasm, becoming organelles like lysosomes &peroxisomes
Chapter 3 – Cell Structure & FunctionLysosomes – contain digestive enzymes
What kind substances do you think lysosomes digest?
Autophagy – digestion of organelles
Autolysis – digestion of their host cell
Perioxisomes – various metabolic tasks dealing with oxidizing organic molecules
Vacuoles – large membranous sacs for storing substances
Chapter 3 – Cell Structure & FunctionEnergy-Related Organelles
Chloroplasts – harness solar energy to synthesize carbohydrates
Mitochondria – utilizing carbohydrates & other energy rich molecules to form ATP –energy currency of the cell
Chapter 3 – Cell Structure & FunctionChloroplast structure
It is a double membrane organelle enclosing a fluid-filled space called the stroma.
Within the stroma are flattened sacs called thylakoids. Stacks of thylakoids are called grana.
The thylakoids are involved in capturing solar energy via pigments like chlorophyll, while carbohydrate synthesisoccurs in the stroma
Chapter 3 – Cell Structure & FunctionMitochondria structure
It is a double membrane organelle enclosing a fluid-filled space called the matrix.
The inner membrane contains the key enzyme ATP synthase which is used to synthesize ATP from the breakdown of energy rich molecules like carbohydrates
Chapter 3 – Cell Structure & FunctionCytoskeleton
It is a network of interconnected filaments & tubules that extends from the nucleus to the plasma membrane
It determines cellular shape & movement
Composed of microtubules, microfilaments, & intermediate filaments
1) Microtubules are composed of the globular protein tubulin. They are important for maintaining asymmetrical cell shape (neurons) & complex cell movements: A) transportation of secretory vesicles within the cell, B) movement of flagella & cilia, & C) distribution of chromosomes during cell division
2) Microfilaments which are composed of the proteins actin (globular) & myosin (golf-club shaped). They are involved in contractile mechanisms (muscle & cytokinesis) contraction & as mechanical stiffeners for several cellular projections (microvilli)
3) Intermediate filaments are highly stable polymers. They primarily support the nuclear envelope & the plasma membrane
Chapter 3 – Cell Structure & Function
Chapter 3 – Cell Structure & FunctionCentrioles – Form the microtubule organizing centers in cell reproduction / division (mitosis). Involved in assembling & disassembling microtubules necessary for mitosis
Chapter 3 – Cell Structure & FunctionCilia & Flagella – cell movement or the movement of substances along the cell surface
Which of your cells contain cilia or flagella?
Chapter 3 – Cell Structure & FunctionEvolution of the Eukaryotic Cell
Endosymbiotic hypothesis – hypothesis involving the engulfing (endocytosis) of prokaryotic cells by a eukaryotic cell, forming some of the key life sustaining organelles within the eukaryotic cell
Chapter 3 – Cell Structure & Function1. Mitochondria & chloroplasts are similar to bacteria in size & structure
2. Both organelles are bounded by a double membrane, in which the outer membrane may be derived from the engulfing vesicle & the inner one from the prokaryotic cell
3. Mitochondria & chloroplasts have a limited amount of genetic material, which is arranged in a circular loop like bacteria
4. They both possess their own ribosomes, which resemble bacterial types, & produce some proteins
5. The RNA base sequence of their ribosomes suggest a bacterial origin
Chapter 2 – The Molecules of CellsPRACTICE QUESTIONS
1. Who coined the term “cellulae” or cell?
2. What does the cell theory state?
3. Why must cells be small?
4. What are all cells composed of?
5. What are the functions of the following structures: plasma membrane, mitochondria, ribosome, peroxisome, Golgi apparatus
6. What are nucleoli, where would you find them, & what is their function?
7. What does the endosymbiotic hypothesis state?
