Cell Structure

By: J. Quigley9/2013

Discovery of Cells

• All life forms on the planet are made from cells

• The bacteria that live in our gut and the cells that make up are body are built from the same machinery

• Cells need to obtain and use energy, respond to their environment and reproduce

Discovery of Cells

• Microscope observations of organisms led to the discovery of the basic characteristics common to all living things.

• In 1665, Robert Hook, an English scientist, created the first microscope

Cell Theory

• There are three rules of cells:– All living things are made up of one or more cells– Cells are the basic units of structure and function

in organisms– All cells arise from existing cells

Looking at Cells

• A cell’s shape reflects the cells function.

• Cells may be flat, round or rectangular. Some cells have irregular shapes while others constantly change shapes… these differences enable cells to perform highly specific functions in the body

Cell Size

• All substances that enter or leave a cell must pass through the surface of the cell. As a cell gets larger, it takes up more nutrients and releases more wastes. These substances must move farther to reach their destination in a larger cell

• Cell size is limited by the cell’s surface area to volume ratio• Scientists can estimate a cell’s ability to exchange materials

by calculating the cell’s surface area to volume ratio… cells with greater surface area to volume ratio exchange substances more efficiently

• Smaller is better.

Cell Shape

• Larger cells often have shapes that increase the surface area available for exchange… such as being broad and flat

Cell Features

• All cells from a bacteria to an apple to a human share common structural features. All cells have:– A cell membrane– Cytoplasm– Ribosomes– DNA

Cell Features

• Cell membrane is the cells outer boundary. It acts as a barrier between the outside environment and the inside of the cell

Cell features

• Cytosol- the fluid inside the cell that is full of dissolved particles

• Cytoplasm- includes the fluid cytosol and most of the structures that are suspended in the fluid

Cell Features

• Ribosomes are cellular structures that make proteins.

• All cells also have DNA, the genetic material that provides instructions for making proteins, regulates cellular activities and enables cells to reproduce

Prokaryotic Cells

• A prokaryote is/has:– Only one cell– Quite simple in

organization – Genetic material is a

single loop of DNA which looks like a tangled string in the center of the cell

– Ribosomes and enzymes share the cytoplasm with the DNA

Prokaryotes

• Scientists think that the first prokaryotes may have lived 3.5 billion years ago or more! For millions of years, prokaryotes were the only organisms on earth.

• They were/are very simple and small and they live in a wide range of habitats

Eukaryotes

• A eukaryote is organism that is made up of one or more eukaryotic cells

• Some are single cells, most are multicellular• Because of their complex organization, eukaryotic cells

can carry out more specialized functions than prokaryotic cells can

• Their DNA is housed in an internal compartment called the nucleus

• Eukaryotes have organelles. Organelles are structures that carry out specific activities/functions within the cell

Eukaryotes

• Primitive eukaryotes first showed up about 1.5 billion years ago and have evolved into the multicellular organisms of today

Framework of the Cell

• The cytoplasm of a eukaryotic cell is packed with all sorts of structures and molecules.

• The cytoskeleton has a web of protein fibers that help the cell move, keep its shape and organize its parts

Directing Cellular Activity

• Almost all cellular activity depends on the proteins the cell makes.

• The instructions for making proteins is in the DNA

• The DNA in eukaryotes is inside the nucleus

• DNA instructions are copied as RNA messages, which leave the nucleus. In the cytoplasm ribosomes use the RNA messages to assemble proteins.

Nucleus• The nucleus stores the cell’s

DNA. • The nuclear envelope is a

double membrane that surrounds and protects the nucleus

• Within the nucleus is the nucleolus.

• The nucleolus is the region in the nucleus that makes ribosomes. The ribosomes pass through the nuclear envelope and into the cytoplasm.

Ribosomes• Each ribosome is made of

RNA and many proteins. • Some ribosomes are found in

the cytosol. These “free” ribosomes make proteins that are to remain INSIDE the cell

• Some ribosomes are attached to another organelle. These “bound” ribosomes make proteins that are to be exported OUTSIDE the cell.

Protein Processing

• Proteins produced by cells have many uses. The proteins that are sent outside the cell must be kept separate from the rest of the cytoplasm. To achieve this separation, the cell packages the protein in vesicles.

• A vesicle is a small, often circular shaped sac that is formed by a membrane

• The endoplasmic reticulum and the golgi apparatus are organelles that prepare proteins for export.

Endoplasmic Reticulum

• The endoplasmic reticulum (ER) is a system of internal membranes that move proteins and other substances though the cell. The membrane of the ER is connected to the outer membrane of the nuclear envelope

Endoplasmic Reticulum

• Rough ER- ribosomes are attached to some parts of the surface of the ER making it bumpy in appearance. As proteins are made they cross the ER membrane, entering the ER, which then pinches off to form a vesicle around the protein

Endoplasmic Reticulum

• Smooth ER- Has no attached ribosomes and is smooth in appearance. Enzymes of the smooth ER perform various functions such as making lipids and breaking down toxic substances

Golgi Apparatus

• The golgi apparatus is a set of flattened membrane-bound sacs that help make and package materials to be transported out of the cell.

• The golgi also makes lysosomes.

Storage and Maintenance

• Vesicles have an important role within the cell. Some transport materials within the cell. Other has important storage roles.

• Vesicles help maintain homeostasis by storing and releasing various substances as the cell needs them.

Storage and Maintenance

• Lysosomes are vesicles that contain specific enzymes that break down large molecules. They digest food particles to provide nutrients for the cell and help recycle materials in the cell by digesting old or damaged organelles.

Storage and Maintenance

• Central Vacuole- many plants contain a large, membrane compartment called the central vacuole. It is a large vacuole that stores water, nutrients and waste.

Storage and Maintenance

• Vacuoles- Many animal cells have much smaller storage vesicles than plants. They store food particles for later use.

Energy Production

• Cells need a constant source of energy. • The energy for cellular functions is produced

by chemical reactions that occur in the mitochondria and chloroplasts.

• Nearly all eukaryotic cells have mitochondria, only plant cells have chloroplasts

Energy Production

• Chloroplasts- an organelle that uses light energy to make sugar from carbon dioxide and water.

• Each chloroplast is surrounded by a pair of membranes, inside the membrane are stacks of flattened sacs. The ATP producing chemical reactions take place inside the sacs.

Energy Production• Mitochondria- organelle that

uses energy from organic compounds to make ATP.

• Mitochondrion have a smooth outer membrane and a folded inner membrane. ATP producing enzymes mostly live in the inner membrane.

• Cells with high energy requirements have more mitochondria than cells with lower energy requirements

Diversity in Cells

• More than 50 million types of organisms live on earth!!!

• Each organism is made up of different types of cells.

• Differences in cells enable organisms to adapt to their natural environments.

Diversity in Prokaryotes

• Prokaryotes vary in shape, the way they obtain and use energy, the make up of their cell walls and their ability to move

• Many prokaryotes have a flagella- a long thread like structure that rotates quickly for movement

Diversity in Eukaryotic Cells

• Eukaryotic cells also vary in structure according to their function. Some organelles are more prominent in some cell types. By varying their internal make up, cells can become specialized for certain functions.

Diversity in Eukaryotic Cells

• Animal and plant cells are two types of eukaryotic cells. Both have many of the same organelles, but plants have chloroplasts, a large central vacuole and a cell wall that surrounds the cell membrane.

Levels of Organization

• Multicellular organisms, such as plants and animals, are made up of thousands, millions or even trillions of highly specialized cells.

• These cells cooperate to perform specific tasks

• They assemble together to form structures called tissues and organs.

Levels of Organization

• Cells make tissues- a distinct group of cells that have similar structure and function

• Tissues make organs- specialized structure that has a specific function

• Organs make organ systems- they carry out major body functions