Introduction to The Cell

Earth is 4.5 Billion Years Old

Cyanobacteria were among the first organisms to exist on planet Earth ~ 3.8 Billion Years Ago

Anatomy of a Bacteria Cell

Cross-Section of a Bacterial Cell

E. Coli Bacteria

Illustration Showing the Anatomy of a Typical Bacteria Cell

The Prokaryotic Cell

Eukaryotic cells Do Have

membrane-bound organelles.
have a true nucleus.

Prokaryotic cells Do NOT Have

DNA in the form of a single circular chromosome called a plasmid.
A nucleoid in which the genetic material resides.

Prokaryotic organisms belong to the Archaea and Bacteria domains of life, whereas eukaryotic organisms belong to the Eukarya domain.

Prokaryotic cells existed from about one-billion years before eukaryotic single-celled organisms evolved. Prokaryotic cells are almost always smaller than eukaryotic cells. Prokaryotic cells lack membrane-bound organelles and do not have a nucleus. In contrast, eukaryotic cells do have a nucleus and do have membrane-bound organelles.

The Cell Membrane (Plasma Membrane)
- The Main Function of the Cell Membrane is TRANSPORT REGULATION -

The cell membrane is also called the plasma membrane. You can think of the membrane as the "skin" of the cell. Anything outside of the cell is considered "extracellular" and the contents inside the cell are considered "intracellular". The cell membrane protects the cell by creating a barrier between what is inside the cell and what is outside the cell.

Cross Section of the Cell Membrane

The cell membrane surrounds the entire cell and act as protection. You can think of the cell membrane as acting like our skin!

In addition to this, the cell membrane does something our skin can’t do... It regulates what comes into the cell and what goes out of the cell. For this reason, we consider the cell membrane to be “SELECTIVELY PERMEABLE” which means that it allows some substances to enter or exit the cell, but not others. This is a very important function.

The Cell Membrane is selectively permeable due to its structure. The cell membrane is made up of a phospholipid bilayer.

Phospholipid

The phospholipid bilayer of the cell membrane has a unique structure. It is made up of an inner layer and an outer layer of phospholipids that are oriented with their 'tails' facing each other.

Phospholipids are considered amphiphilic, because they contain a polar, hydrophillic head that consists of a phosphate group and two nonpolar, hydrophobic fatty acid chains as 'tails'.

When the phospholipids form the cell membrane, the polar, hydrophillic (water-loving) heads are oriented towards the liquid outside the cells (extracellular fluid) and the liquid inside the cell (intracellular fluid). The tails of the phospholipids are oriented towards each other, away from the liquid, since they are made up of hydrophobic (water-fearing) fatty acid chains. This formation creates a barrier between the extracellular matrix and the intracellular fluid (cytoplasm).

Click Below to View a Video on the Mighty Membrane

Vesicular Transport
exocytosis = secretion and endocytosis = uptake

Endocytosis
Brings Things INTO the Cell.

"Endo-" means "inside". "Cyto-" means "cell". The suffix (or the last part of the term) is "-osis" which means "a process". So, the word endocytosis, is literally the process by which the cell takes contents from the extracellular fluid and brings it INSIDE the cell.

https://media.giphy.com/media/JCnzPniDIsuHu/giphy.gif

TIP: By breaking scientific terms down into their Greek and Latin roots, the name gives us the function! This is a great thing to know when you 'blank out' on that exam question!

Endocytosis is the process by which contents from the extracellular matrix are taken up INTO the cell through a mechanism that involves the cell membrane essentially "pinching off" part of itself to form a vesicle that surrounds the particles being transported into the cell.

Exocytosis
Moves Things OUT OF the Cell.

"Exo-" means "outside". "Cyto-" means "cell". The suffix (or the last part of the term) is "-osis" which means "a process". So, the word exocytosis, is literally the process by which the cell transports contents from the inside to OUTSIDE the cell.

EXCOCYTOSIS: source: https://giphy.com/gifs/biology-dictionary-12ePDWqxENNjgc

Exocytosis is when a vesicle from inside the cell fuses with the membrane and the contents are released into the extracellular fluid.

Contents go OUTSIDE the cell.

VESICLES

A vesicle is basically a small circular piece of the cell membrane. It may have come from the cell membrane directly, as in endocytosis, or can be generated from membranes of membrane-bound organelles. The function of vesicles in the cell is transportation.

Vesicular transport is a vital part of the cell's function. Vesicles perform a variety of functions, including transport, metabolism, and temporary storage .

There are 3 different types of endocytosis.

Phagocytosis – “cell eating” - In phagocytosis, one cell will engulf the target and then proceed to digest or destroy the contents of the vesicle. Phagocytosis is demonstrated by white blood cells that are appropriately named, "phagocytes".
Pinocytosis – “cell drinking” - Cells tend to sample small amounts of the extracellular fluid via pinocytosis. Pinocytosis is when the endocytosis results in a vesicle having only extracellular fluid as its contents.
Receptor-mediated endocytosis - This occurs when the plasma proteins bind only to certain molecules via a "lock and key" mechanism. The binding triggers the section of the membrane to "invaginate" and form a vesicle around the molecule that transports it into the cell from the extracellular fluid.

Receptor-Mediated Endocytosis

GIF Courtesy of Source s10.lite.msu.edu

Endocytosis and Exocytosis

GIF Courtesy of Source s10.lite.msu.edu

via GIPHY

Vesicle
The Main Function of the Vesicle is Transport

By SuperManu - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2918850

The vesicle consists of a small amount of fluid (and sometimes particles) surrounded by a phospholipid bilayer. This bilayer is made up of the same phospholipids that are found in the cell membrane of the plasma membrane. this is due to the fact that vesicles are actually made from the cell membrane itself!

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Nucleus
The Main Function of the Nucleus is to Hold the DNA.

The nucleus is like the "brain" or the "command center" of the cell. This is due to the fact that the nucleus holds the DNA. The DNA acts as the cell's "instruction manual" which has the instructions for all of the functions of the cell, as well as the instructions for growth, development and cellular reproduction!

The structure of the nucleus - The nucleus is surrounded by the nuclear envelope, which is essentially a membrane (a phospholipid bilayer) that compartmentalizes (or separates) the nucleus from the rest of the cell. The liquid inside of the nucleus is called the nucleoplasm.

DNA stands for deoxyribonucleic acid. It is the "instruction manual" for the cell. The primary function of the DNA is to provide the instructions for protein synthesis to the cell through the processes of transcription and translation.

Nucleolus
The Main Function of the Nucleolus is to Make Ribosomes

The nucleolus is located inside of the nucleus. It is the largest structure residing inside of the nucleus. Its primary function is to make ribosomes.

Electron Micrograph of a nucleus and nucleolus in an animal cell.

By Image from An Owner's Guide to the Cell // National Institute of General Medical Sciences, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2101429

Ribosomes
The Main Function of a Ribosome is to Be the Site of Protein Synthesis.

After the ribosome is assembled (made) in the nucleolus, it leaves the nucleus. Some ribosomes will end up as "free ribosomes" that remain unattached in the cytosol. Other ribosomes will attach to the nearby Rough Endoplasmic Reticulum.

All ribosomes function as "the site of protein synthesis". Free ribosomes are used as the site for making water-soluble proteins, whereas the ribosomes that are attached to the rough endoplasmic reticulum act as the site for making proteins that will either be incorporated into the cell membrane or will be transported out of the cell (via exocytosis).

ENDOPLASMIC RETICULUM

There are 2 types of endoplasmic reticulum (ER); the rough endoplasmic reticulum and the smooth endoplasmic reticulum.

The Rough Endoplasmic Reticulum
(The Rough ER)

The rough ER gets its name from its 'bumpy' or 'rough' appearance due to ribosomes that are attached to it. In the rough ER, ribosomes are assembled in the nucleolus and then exit the nucleus. Some of these ribosomes then attach themselves to the rough endoplasmic reticulum, where they will act as a "site of protein synthesis" for the cell.

The Smooth Endoplasmic Reticulum
(The Smooth ER)

The smooth endoplasmic reticulum (Smooth ER) appears smooth in comparison to the rough ER. This is because the smooth ER does not have ribosomes bound to it. The smooth ER's main function is to make lipids.

The Golgi Body

Lysozyme

Cell Wall

Summary of Structure and Function of Organelles

ORGANELLE or STRUCTURE	FUNCTION	SIMILAR TO
NUCLEUS	HOLDS THE DNA	INSTRUCTION MANUAL
NUCLEOLUS	MAKES RIBOSOMES	FACTORY
MEMBRANE	PROTECTION - REGULATION OF TRANSPORT	SKIN
GOLGI BODY	MODIFIES, PACKAGES AND SHIPS PROTEINS	POST OFFICE
MITOCHONDRIA	CREATES ENERGY (ATP)	POWER PLANT
ROUGH ENDOPLASMIC RETICULUM	HAS RIBOSOMES
SMOOTH ENDOPLASMIC RETICULUM	LIPID PRODUCTION AND CALCIUM STORAGE
PEROXISOME	DETOXIFIES	GARBAGE DISPOSAL
LYSOSOME	DIGESTS UNWANTED SUBSTANCES	RECYCLING CENTER
RIBOSOME	THE SITE OF PROTEIN SYNTHESIS	ASSEMBLY LINE
NUCLEOPLASM	LIQUID OF THE NUCLEUS
NUCLEAR ENVELOPE	MEMBRANE AROUND THE NUCLEUS	"SKIN" OF NUCLEUS
VESICLES	TRANSPORTATION	VEHICLES
CYTOSOL	LIQUID OF THE CELL THAT LIES INSIDE OF THE CELL MEMBRANE, AND OUTSIDE THE NUCLEUS