Sec 4- Structure and Function of Cells

Question 1

What is a cell?

Answer 1

A cell is the basic unit of life.
All cells have:
1. A border: plasma membrane (or cell membrane)
2. Interior: cytoplasm (cytosol)
3. Information/instructions: DNA
4. Protein factories: ribosomes

Question 2

Nucelus vs Nucleoid

Answer 2

All cells are classed as eukaryotes or prokaryotes based on how DNA is housed in the cell.

Nucleus
* Organelle with membranes that holds a eukaryotic cell’s DNA
* Nuclear membrane or nucelar envelope
* “Eu” = true
* “-karya” = kernel

Nucleoid
* Region of cytoplasm where DN is concentrated in a prokaryotic cell.
* “Pro” = before; olrder cells, evolved before the nucleus.
* “-karya” = kernel

Question 3

What are organelles?

Answer 3

Cell metabolism occurs in cytoplasm and internal compartments, including organelles.

• Structure that carries out a specialized metabolic function inside a cell (“little organ”).
• Ex: mitochondrion, chloroplast, ribosome
• Most organelles are found in eukaryotic cells, some also in prokaryotic cells
• Can be membrane-bound or not.

Question 4

Why must cells be small?

Answer 4

Cells must be small to efficiently exchange materials with their environment.

• Surface-to-volume ratio limits cell size and influecnes cell shape.
• How small?
• Prokaryotic ~ 1 um
• Eukaryotic ~ 100 um
• Surface-to-volume rations- a relationship in which the volume of an object increases with the cube of the diameter (4/2pir^3), but the surface areas increases with the square (4pir^2).

Question 5

What is microvilli?

Answer 5

This increases the surface area of the cells lining the small intestine to aid in absorption of nutrients.

Question 6

Why are microscopes important?

Answer 6

No one knew cells existed until microscopes were invented.

• 1600s: Antonie van Leeuwenhoek’s microscope
• 1600s: Robert Hooke improved the microscope and coined the term “cell”.
• He looked at cork cells.
• 1830s: Matthias Schleiden (plant cells) and Theodore Schwann (animal cells) realized cells were alive and proposed the cell theory.

Question 7

What are modern microscopes?

Answer 7

Different types of micrschopes “hit” the specimen with either light or electrons.

• Light microscope- living cells, cells and large organelles (um)/1,000x smaller than eye
• Electron microscopes- killing and perserving cells, virsues and large molecules (nm)/100,000 x smaller than eye
• Transmission electron microscope
• Scanning electron microscope
• A photo taken while looking through a micrscope is called a micrograph.

Question 8

What is the plasma membrane?

Answer 8

A plasma membrane surrounds the cell and controls which substances move in and out: selectively permeable.

• A cell’s outermost membrane
• Also called the cell membrane
• Composed of phospholipids

Question 9

What is the lipid bilayer?

Answer 9

Structural foundation of cell membranes; arranged tail-to-tail in a bilayer.

• The hydrophobic tails of both layers are sandwiched between the hydrophilic heads.

Question 10

The Fluid Mosaic Model

Answer 10

The plasma membrane is a mosaic of phospholipids and proteins that are able to move freely around the membrane.

Question 11

What are membrane proteins?

Answer 11

• Transport proteins help specific ions or molecules across the membrane (selective permeability).
• Enzymes speed chemical processes.
• Adhesion proteins help cells stick together.
• Recognition proteins ta cels as “self”.
• Receptor proteins bind to a particular substance outside the cell.

Question 12

Prokaryotic Cells Overview

Answer 12

Domains/kingdoms Bacteria and Archae make up the prokaryotes.
Prokaryotes are all single-celled organisms with no nucleus.

Features:
* cell wall
* flagella or pili
* ribosomes
* nuceloid region
* plasmid(s)

Question 13

What is the prokaryotic cell wall?

Answer 13

• Semirigid but permeable strcture that surrounds the plasma membrane of some cells.
• determined shape of bacteria
• In bacteria it consists peptidoglycan (protein & sugar).

Antibiotics
* Target prokaryotic cells (bacteria); penicillin disrupts the formation of the bacterial cell wall.

Question 14

What are flagella and pili?

Answer 14

Flagellum- Long, slender cellular structure used for mobility.
Pilus- A protein filament used to help cells attach to surfaces.
* some involved in bacterial sex

Question 15

What is the cytoplasm of prokaryotes?

Answer 15

Ribsomes- Organelle of protein synthesis.
Nucleoid region- Contains circular DNA (genomic DNA). Also called circular chromosome.
Plasmid(s)- Extra piece of circular NDA that contains extra genes, like those for antibiotic resistance (like penicillin resistance!).

Question 16

The inside of the eukaryotic cells?

Answer 16

1. Nucleus
2. Ribosomes
3. Endomembrane system organelles
   A) Endoplasmic reticulum (rough and smoooth ER)
   B) Vesicles, peroxisomes, vacuoles, and lysosomes
   C) Golgi apparatus/body/complex
4. Mitochondria
5. Chloroplasts (plant/algae cells)
6. Cytoskeleton
7. Appendages
   A) Cilia
   B) Flagella
   C) Pseudopods

Question 17

What is the nucleus?

Answer 17

• Not technically part of cytoplasm.
• Double lipid bilayer is called nuclear membrane or nuclear envelope.
• It has nuclear pores so that substances can go in and out of the nucleus.
• Houses DNA, which is wound around histone proteins to make chromatin.
• Chromatin condenses during cell replication and is visible as chromosomes.
• Eukaryotic chromosomes are always linear and there is more than one.
• Unraveled DNA in one human cell is 2 meters long! (250 times to sun & back).
• RIbosomes are assembled in a region of the nucleus called the nucleolus (not membrane-bound).

Question 18

What are ribosomes?

Answer 18

Ribosomes build all the cell’s proteins; they are protein “factories”.

• There are two locations for ribosomes
• “Free” ribosomes in the cutoplasm produce proteins that will remain there (domestic).
• Ribsomes on the ER produce proteins to be part of membranes or secreted from the cell (exports).

Question 19

What is the endoplasmic reticulum (ER)?

Answer 19

A continuous system of sacs and tubes that is an extension of the nuclear envelope.

• Part of the endomembrane system.
• Rough ER is studded with ribsomes.
• Smooth ER has no ribsomes.

Question 20

What is the rough ER?

Answer 20

The function of the rough ER is to produce proteins (via the ribsomes) that are going to be excreted or placed in the plasma membrane.

• The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane.

Question 21

What is the smooth ER?

Answer 21

The smooth ER produces lipids, including steroids like the sex hormones (testes and ovaries).
* Also produces carbohydrates.

• The smooth ER lacks surface ribsomes.
• Smooth ER in the liver is involved in detoxification of drugs and other poisons in the bloodstream.

Question 22

What are vesicles?

Answer 22

Small, membrane-enclosed, saclike organelle.
Stores, transports, or degrades its contents.

Peroxisome
* Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances.
Lysome
* Vesicle with enzymes for intracellular digestion.
1. fuses with food vacuoles to digest food
2. break down damaged organelles
3. break down bacteria (WBCs)
4. sculpting function (webbing) through programmed cell death

Question 23

What are lysomoal storage diseases?

Answer 23

Aperson is missing digestive enzymes of lysosomes.
Most are fatal in early childhood.

1. Pompe’s Disease: lack of enzyme that digests the polysaccharide glycogen in muscle cells; causes muscle weakness, especially in the hearts; leads to heart failure.
2. Tay-Sachs Disease: lack of enzyme that digests lipids; nerve cells accumulate excess lipids in the brain.

Question 24

What is the large vesicle: vacuole?

Answer 24

A fluid-filled organelle that stores or disposes of wastes, debris, or toxic materials.

• Common in plants, where the central vacuole contains water and causes turgor pressure, which maintains the shape of the plant.
• In animals adipose tissue has vacuoles that store fat.

Question 25

What is golgi body?

Answer 25

Organelle that modifies proteins and lipids?