Cells

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Cells Cells are small. There are 100 trillion cells in the body. They range in size from 7.5 µm =

micrometers (micrometer is 1 millionth of a meter) to 250 µm, which is visible to the naked eye.

There are thousands of types of cells, each is specialized for a task: skin, liver, kidney, etc.

Each cell has specialized structures for their function.

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Cells

Every cell has three things in common: Metabolic functions (using nutrients such as

sugars and oxygen, and creating waste products) Responds to its environment Capable of maintaining homeostasis within itself

and within the body.

HOMEOSTASIS is maintaining a constant and appropriate internal environment, such as temperature, pH, and glucose levels.

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Introduction to Cells All cells have several main components

Plasma membrane Cytoplasm and cytosol Nucleus Organelles (are surrounded by a

membrane) Ribosomes (are not surrounded by a

membrane)

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Structure of a Generalized Cell

Figure 2.1

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Cytoplasm and CytosolCYTOPLASM: the watery liquid inside and outside the

organelles, but outside the nucleus. NEUCLEOPLASM: the liquid inside the nucleus. CYTOSOL: another liquid that is thicker than water, and

is NOT inside the organelles. It is only found outside of the organelles and nucleus.

Cytosol contains the following: Mostly water Things dissolved in water (amino acids, sugars like glucose,

nucleic acids, and ATP, which is a molecule used for energy). Cytoskeleton: made up of long protein fibers, extend

throughout cytosol.

Function of cytoskeleton:1) Maintains cell shape2) Movement (such as muscle cell contraction,

organelles within the cell, or the cell itself moving around).

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Cell Membrane The cell membrane is semi-permeable

to allow only certain things into and out of the cell.

Functions of the Plasma Membrane: Movement of materials into and out of

cell, and acts as a barrier to the external environment

Acts as a site for receiving signals from the rest of the body

Helps hold the cell in place

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Plasma (cell) Membrane The plasma (cell) membrane is made up of two

layers of molecules = PHOSPHOLIPIDS. It’s therefore called a phospholipid

bilayer Phospholipids are amphipathic molecules. That means they have one end that has an

affinity for something and another end that does not have an affinity to that substance. In this case, the affinity is to water.

A substance that likes water is called HYDROPHILIC (likes water).

A region of a molecule that is hydrophilic is called a POLAR region.

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Plasma (cell) Membrane

A substance that dislikes water is called HYDROPHOBIC (afraid of water).

A region of a molecule that is hydrophobic is called a NON-POLAR region.

Therefore, the phospholipids, being amphipathic, will have a polar region and a non-polar region.

The polar region is the PHOSPHATE HEADS The non-polar region is the FATTY ACID

TAILS .

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Phosphate heads

Fatty Acid tails

The cell membrane is like a film of oil on water. Is oil flexible? (yes) Is oil strong? (no) But it prevents materials from going across into the water.

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PLASMA MEMBRANE

Plasma (cell) Membrane The plasma membrane has proteins in it that

are made in the RIBOSOMES and transported to the cell membrane in this case (other proteins are carried elsewhere).

Ribosomes carry out the three functions of the plasma membrane.

Around each organelle is a membrane identical to the plasma membrane except for the proteins.

Each cell has hundreds of membranes. Ribosomes are not organelles because they do

not have a plasma membrane.

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The Cell Membrane

Figure 2.2a

Phospho-lipid Bilayer

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Endoplasmic Reticulum The ER is a network of channels. Two types:

Rough ER: contains ribosomes Function of ribosomes is to make proteins.

Smooth ER: no ribosomes Function is to detoxify chemicals that enter

the cell.

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ROUGH ENDOPLASMIC RETICULUM (endoplasmic = within cytoplasm; reticulum = network; rough = surface of membrane covered with ribosomes. This is an organelle, but the ribosomes are not.

Function of RER is the synthesis (making) of proteins: a. Membrane proteins b. Proteins for export (such as digestive

system enzymes)c. Proteins for use within the cell

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SMOOTH ENDOPLASMIC RETICULUM (no ribosomes)

Function of SERa. SER is continuous with the rough ER, but lacks ribosomes and has several functions

1) Detoxifies harmful substances (alcohol, drugs, medicines)

NOTE: in CSI, when they suspect poisoning, they first look at the SER in the liver.

2) Stores calcium3) Involved in lipid production (lipid bodies)

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The Endoplasmic Reticulum and Ribosomes

Figure 2.5

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Golgi Complex When the proteins have finished their journey

in the RER, their edges are exposed, and are vulnerable to oxidative damage. Therefore, they first go to the Golgi complex, which puts chemical bonds on the ends of the proteins.

Thus, in the Golgi complex, the proteins are modified and prepared for transport out of the cell.

The Golgi complex is like a Fed-Ex center that packages and ships the proteins that were made in the ribosomes.

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Golgi Apparatus

Figure 2.8

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RER to Golgi Complex

Vesicles Vesicles (vacuoles) are bubble-like

containers for various substances. Some are created by the end of the Golgi complex: a piece of membrane pinches off, leaving a protein in the vesicle, which carries the protein to the cell membrane, where it merges with the cell membrane, pops, and releases its contents outside of the cell.

Other vesicles are storage containers for food or enzymes.

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VesiclesVESICLES: a sphere of membrane with something

in it. This is an organelle. Many types: LYSOSOMES: are sacs of powerful digestive enzymes to

dissolve an old organelle, bacteria, or foreign debris. They are also used to commit cell suicide (APOPTOSIS is the term for programmed cell death). When bacteria enter a cell, the lysosome will fuse with the

bacteria and release its enzymes on them to destroy them. TRANSPORT VESICLES: when material needs to move

from RER to Golgi complex, or from Golgi complex to cell membrane, etc. STORAGE VESICLES: one vesicle may store

carbohydrates, one may store lipids, one may store enzymes.

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Disorder of Lysosomes Tay–Sachs disease A genetic disorder that causes deterioration

of mental and physical abilities that commences around six months of age and usually results in death by the age of four.

Caused by insufficient activity of an enzyme needed by lysosomes to break down phospholipids.

The lipids accumulate in the brain.

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Mitochondria Mitochondria are considered the smallest

living units in the body because they can make their own energy (ATP). Cells have hundreds of mitochondria.

Function of mitochondria is to make most of the cell’s ATP, which is cellular energy (ATP is an energy source).

Some ATP is made in the cytosol, but most is made in the mitochondria.

NOTE: Mitochondria must have OXYGEN to convert nutrients to ATP for energy.

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Mitochondria Mitochondria –

generate most of the cell’s energy (ATP); most complex organelle.

Contains curves known as cristae that can be seen under a microscope.

Figure 2.9

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Mitochondrial DNA (mtDNA) Nuclear and mitochondrial DNA are thought

to be of separate evolutionary origin, with the mtDNA being derived from the DNA of the bacteria that were engulfed by the early ancestors of today's eukaryotic cells.

mtDNA is inherited from the mother (maternally inherited).

This enables researchers to trace maternal lineage far back in time.

Fun Facts

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Mitochondrial DNA Biologists can determine and then compare

mtDNA sequences among different species and use the comparisons to build an evolutionary tree for the species examined.

Studies have used mtDNA to trace the ancestry of domestic dogs to wolves.

However, they have recently found that the Sabre-tooth tiger is not the ancestor of the domestic cat.

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Nucleus

NUCLEUS: Usually the largest structure in a cell. It does not contain cytoplasm; it is called nucleoplasm.

The nuclear membrane contains pores, called nuclear pores. These allow certain materials into and out of the nucleus.

Functions of the nucleus: Stores DNA (chromosomes are made up of DNA) Makes RNA (RNA is the code for making a protein.

It is copied from DNA).

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The Nucleus

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Nucleolus Within a nucleus there are areas that are

darker. These are regions of condensed RNA. Remember, the function of the RNA is to carry copies of the genes for proteins to the ribosomes.

The nucleolus is NOT an organelle, but the nucleus is. Don’t get “nucleolus” mixed up with the word “nucleus” on the test. The nucleolus does not contain the DNA; the nucleus does. The nucleolus is within the nucleus, but it does NOT contain DNA.

The nucleolus contains RNA, which is important for protein synthesis.

Do not get nucleus and nucleolus mixed up!

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Centrioles Centrioles are filaments within the cell

that function during mitosis. When the cell goes from metaphase to

anaphase of mitosis, the chromatids separate and follow the spindles of the centrioles towards the opposite ends of the cell.

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Centrioles

Centrioles

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Flagellum Some cells have a flagellum, which is a

whip-like tail used to help them move (locomotion).

An example is a sperm cell.

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Microvilli Some cells have microvilli on their cell

membrane, which increase the surface area of cells by approximately 600 fold, thus facilitating absorption and secretion.

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Cilia Some cells have cilia, which are small, hair-

like structures that can wave back and forth, causing substances to move along across the top of the cell.

For example, the cells of the lungs are lined with cilia, which move mucous up from the lungs so it can be coughed up and swallowed.

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Cell Cycle CELL CYCLE: the life cycle of a cell.

Some cells never divide (neurons). When getting ready to divide, cells

undergo MITOSIS to make one cell into two.

Some cells divide rapidly (every few days), some rarely (every 1-2 months), some never.

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Stem Cells STEM CELLS: A population of cells are always

available to replace the cells that died. Muscle stem cells give rise to new muscle

cells. Bone marrow stem cells give rise to new blood

cells. Embryonic stem cells give rise to any type of

cells, including neurons (adults don’t have neural stem cells) and pancreatic cells (diabetics don’t have pancreatic stem cells).

Stem cells are named by type + suffix: BLAST Erythrocyte = RBC. Erythroblast = stem cell

that gives rise to an erythrocyte.

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Mitosis Overview

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Human Cell Division All cells in our body divide by duplicating

their chromosomes and then splitting into two cells, a process called mitosis

Mitosis produces two daughter cells with the same number and kind of chromosomes as the parent cell.

If a parent cell has 46 chromosomes prior to mitosis, how many chromosomes will the daughter cells have?

Answer = 46. This condition is called diploid (2n).

Sex Cells (Gametes; egg and sperm cells)

After mitosis, sex cells undergo another cell division without duplicating the chromosomes. This is called meiosis: each daughter cell has only half of the chromosomes.

In males, it produces the cells that become sperm

In females, it produces the cells that become eggs.

The sperm and the egg are the sex cells, or gametes.

GAMETES contain half the number of chromosomes compared to the rest of the body cells (23 chromosomes).

This condition is called haploid (n).

Mitosis Stages

Interphase: Chromosomes duplicate stage)

Prophase: Chromosomes shorten and thicken.

Metaphase: Chromosomes line up in the middle of the cell

Anaphase: Chromosomes pull apart Telophase: Cytoplasm divides in two,

forming two daughter cells

Video Clip of Mitosis

MEIOSIS Meiosis only occurs in the testes and

ovaries when they are ready to make an egg cell or a sperm cell.

First, mitosis occurs as normal. But right after that, the two daughter

cells divide again (meiosis), but this time there is no reproduction of the chromosomes.

Crossing OverDuring meiosis, when the second cell

division is at the metaphase stage, the chromosomes touch each other and exchange a few genes.

The exchange of genetic material between chromatids is called crossing-over.

That is what allows for genetic variation.

Crossing Over

MEIOSISMeiosis results in four daughter cells,

each having half the number of chromosomes as the parent cell.

The daughter cells are not genetically identical, and neither is identical to the parent cell.

For example, in MEIOSIS, if the parent cell has 46 chromosomes, the GAMETE will have 23.

It will be haploid (n).

Gametes to Zygote When a sperm and egg (gametes)

combine and contribute their chromosomes, the fertilized egg (called a zygote) will now have 46 chromosomes again.

It will be diploid (2n).

Nondisjunction

Chromosomes can become abnormal if the sister chromosomes do not separate properly during meiosis. This is called nondisjunction.

Video Clip of Blastula

The rate of cell division is close to the rate of cell death.

200 billion erythrocytes die every day, so 200 billion erythrocytes have to be made every day.

Too few = anemia; too many is also a problem.

Body needs to do two things: Control the rate of cell division Control the rate of cell death (apoptosis)

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TumorsTUMOR (an abnormal growth from excess

cells). Two types of tumors: BENIGN (“harmless”, although can cause

harm by pressing on vital structure) MALIGNANT (cancerous). These are

dangerous because the cells in the tumor METASTASIZE (leave original site, go elsewhere and grow).

Cancer is hundreds of diseases, each with a different cause, symptoms, treatment, and prognosis. Any cell type can become malignant, producing different types of cancer.

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Cancer

FOUR TYPES OF CANCER CARCINOMA: epithelial tissue SARCOMA: Connective tissue (bones,

muscles, organs) LYMPHOMA: Lymph nodes LEUKEMIA: Blood or blood-forming

tissues

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Cancer How do you distinguish between

cancers? If there’s a tumor in the lung, BIOPSY

(take a sample of cells, examine under a microscope to see what kind of cells they are).

If pancreas cells are in lung tumor, indicates pancreatic cancer.

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Inner Life of a Cell http://multimedia.mcb.harvard.edu/anim

_innerlife.html

Click on Super Speed

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