cell dan fungsi

Chapter 3 – Cell Structure & Function

History 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


Development 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


Cell size


Why 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


What 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


Cells 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


What 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 synthesize

ribosomes necessary for protein

synthesis


The 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


Golgi 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 embedded

in the plasma membrane

Other vesicles will remain in

the cytoplasm, becoming

organelles like lysosomes &

peroxisomes


Lysosomes – 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


Energy-Related Organelles

Chloroplasts – harness solar energy to synthesize carbohydrates

Mitochondria – utilizing carbohydrates & other energy rich molecules to form ATP –

energy currency of the cell


Chloroplast 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 synthesis

occurs in the stroma


Mitochondria 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


Cytoskeleton

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


Centrioles – Form the microtubule organizing centers in cell reproduction / division

(mitosis). Involved in assembling & disassembling microtubules necessary for mitosis


Cilia & Flagella – cell movement or the movement of substances along the cell surface

Which of your cells contain cilia or flagella?


Evolution 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


1. 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 Cells

PRACTICE 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?

cell dan fungsi

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