Cell Structure and Organelles

Anna Niles and Nora Viniotis

Background on Cells

• Robert Hooke discovered cells in the late 1600’s by observing cork.

• Cells are primarily made up of carbon, oxygen, hydrogen, and nitrogen and a small amount of iron, sodium and potassium.

• Cell size varies. They can be anywhere from 2 micrometers to 1 meter.

• Cell shape varies. They can be disk-shaped, threadlike, toothpick, cubed, etc.

• All cells help perform bodily functions and a cell’s structure reflects its function.

• Cells have 3 main parts: nucleus, cytoplasm, and plasma membrane.

Nucleus

• Contains the genes (DNA) of the cell

• The shape of the nucleus depends on the shape of the cell

• The nucleus has 3 parts: nuclear envelope, nucleolus, and chromatin

Nuclear Envelope• The nuclear envelope consists of both the inner and outer

membranes of the nucleus. It holds the fluid (nucleoplasm), nucleoli, and chromatin within it

• The middle of the 2 membranes contains fluid. Where the 2 membranes touch, they fuse and create nuclear pores

• The nuclear envelope is selectively permeable, with relatively large nuclear pore openings

Nucleolus

• Plural nucleoli• Some cells have

multiple nucleoli• It’s main function

is to produce ribosomes

• Also called “micronucleus”

Chromatin

• Chromatin look like weaving noodles spread throughout the nucleus

• They are made up of DNA and protein

• When the cells divide, the chromatin condenses to form chromosomes

Cytoplasm

• The cellular contents between the nucleus and the cellular membrane

• The cytoplasm has 3 major parts: cytosol (the fluid that suspends the organelles), organelles (the many “factories” that carry out special functions), and inclusions (not always present, but they are the stored nutrients or products)

Cytoplasmic Organelles

• All the “little organs” performing their special job besides the nucleus

• Many organelles have their own membrane to separate themselves from the sometimes very different environment of the surrounding organelles so they can perform their unique function

• The organelles differ from cell to cell, but the following are the general features

Endoplasmic Reticulum

• The mini circulatory system of tubules that spreads throughout the cytoplasm

• It primarily transports proteins• The ER comes in 2 forms:

– Rough ER• Gets the name “rough” ER because it is covered in

ribosomes• All of the cellular membranes are formed from it. And after

they are made, they are sent to other areas

– Smooth ER• Its function is cholesterol synthesis and breakdown, fat

metabolism, and detoxification of drugs

Golgi Apparatus

• Located close to the nucleus, its function is to manage the proteins (send them to their final destination)

• When protein headed for a certain destination collects and the area becomes swollen, it will pinch off (forming a secretory vesicle) and head for the plasma membrane. When they reach the membrane, they fuse with it and rupture, thus releasing their contents out of the cell

Ribosomes

• They are round organelles of protein and RNA

• They are the location of protein synthesis

• Some ribosomes float around in the cytoplasm while others are attached to membranes

• Those attached to membranes are called rough endoplasmic reticulum

• “Soma” means body in Greek

Lysosomes

• They are membrane bound “bubbles” containing digestive enzymes

• Lysosomes demolish worn out or non-usable cell structures

Peroxisomes

• Also membrane bound “bubbles”

• They detoxify harmful substances and disable fire radicals (highly reactive chemicals with unpaired electrons that scramble protein and nucleic acids’ structures)

Cytoskeleton

• Structure of protein that functions as the cell’s skeleton

• The cytoskeleton determines the shape of the cell and provides the necessary components for movement and intracellular transport

• It is made up of intermediate filaments, microfilaments, and microtubules to carry out its functions

Centrioles

• They are made of microtubules• Important in cell division: they direct the creation

of the mitotic spindle (part of mitosis and DNA)

Cellular Extensions

• The part of the cell that enables movement

• Most cells have cilia which are many small whip-like structures that facilitate the movement of substances along the cell’s exterior

• Some cells (such as sperm cells) have flagella, which is a single extension much longer than cilia which is tail-like and propels the cell

Mitochondria

• Sausage-shaped organelles that have double thick membranes

• The outside is smooth, however, the inside has shelf- like projections called cristae

• Enzymes are dissolved within the mitochondria and the reaction of oxygen to break down food also occurs at this site (they are the centers for cellular respiration)

Cellular Respiration• A three step process where our gases are exchanged (oxygen is

used and carbon dioxide is released) to make the energy we need called ATP to perform our everyday functions

• The biggest goal of cellular respiration? ATP!!

1. Glycolysis

• What is it? The breaking down of glucose (a sugar that our body finds from the food

we consume) into 2 pyruvic acids

• Where does it happen? Outside the mitochondria in the cytoplasm

• Goal? 2 pyruvic acids and a small amount of ATP

Transition Reaction

• The reaction between glycolysis and the Kreb’s cycle that occurs only when oxygen is present

• It transforms the 2 pyruvates into 2 acetyl CoA so it can enter the Kreb’s cycle

2. Kreb’s Cycle• What happens? The 2

acetyl CoA feed into this complicated set of reactions to form these electron acceptors (NADH and FADH2) for the next step; CO2 is formed as a waste

• Where does it happen? Inside the mitochondria

• Goal? A few NADH, FADH2 and CO2 molecules, and a small amount of ATP

3. Electron Transport Chain

• What happens? The electron carriers produced in the Kreb’s cycle donate their electrons who “fall down” this chain of proteins to produce ATP

• Where does it happen? Inside the inner membrane of the mitochondria

• Goal? Lots of ATP!

Quiz!