Cells 1: Cell Size and Endomembrane System

Question 1

Why are cells so small?

Answer 1

• Because chemical reactions in cells require diffusion (molecules cannot travel far distances because of their ‘random walk’)
• increases surface area and decrease volume (makes chemical processes more efficient)

Question 2

Describe a prokaryotic cell

Answer 2

• are very small
• have no nucleus
• have few membrane enclosed compartments
• can eat a wide variety of things and can live without oxygen
• has ability to adapt to many different environments and eat toxins

Question 3

Describe a eukaryotic cell

Answer 3

• monophyletic (single ancestor)
• has a membrane-enclosed nucleus and many other membrane-enclosed compartments called organelles
• larger than prokaryotes
• individual chemical reactions occur

Question 4

Difference between plant and animal cells

Answer 4

Mostly the same organelles, but plant cells have:

• cell walls (therefore they do not need sodium potassium pumps because they cannot burst. Instead they wilt when they are dehydrated)
• chloroplasts
• vacuoles (hold water)

Question 5

What does the endomembrane system do?

Answer 5

• it is the primary center for protein and lipid synthesis and processing in eukaryotic cells

Question 6

Describe the nucleus

Answer 6

• is a densely packed section filled with chromosomes where DNA is replicated
• DNA is transcribed into mRNA or rRNA by RNA polymerase
• rRNA ois not translated; it directly folds into a 3D-structure
• Ribosomes are made of 4 rRNAs and about 80 proteins in the nucleolus
• RNAs largely determine structure and function

Question 7

Describe the rough endoplasmic reticulum

Answer 7

• has little individual ribosomes all over the surface

- membrane proteins are made here

Question 8

What are nuclear pore complexes?

Answer 8

• holes all over the nuclear envelope where materials are shipped in and out of the nucleus

Question 9

Describe the signal sequence

Answer 9

1. Signal sequence is synthesized
2. Signal binds to SRP
3. SRP binds to receptor
4. Protein is synthesized into endoplasmic reticulum
5. Protein Synthesis complete

Question 10

Describe the smooth endoplasmic reticulum

Answer 10

• lipids made here (lipids have a half life, dead ones are constantly removed)
• increase surface area
• in the liver the SER is bigger to aid in detoxifying the body by making chemicals more water soluble

Question 11

Describe the golgi apparatus

Answer 11

• has a particular orientation; the cis side faces the ER and the trans side faces plasma membrane
• is a stack of membranes
• olgiosacchride chains added in the golgi
• decides where the proteins need to go

Question 12

Describe the secretory pathway

Answer 12

1. Ribosome deposits protein in ER
2. Protein exits ER
3. Protein enters the golgi apparatus
4. Proteins exit the golgi
5. Proteins exit the cell through exocytosis

Question 13

Describe the process of receptor-mediated endocytosis

Answer 13

1. Macromolecules bind to the receptor
2. Early endosome forms
3. Processing occurs (depends on the macromolecule)
4. Digestive enzymes recieved
5. Mature lysosome forms

Question 14

Describe the process of phagocytosis

Answer 14

1. Detection
2. Phagosome formation
3. Delivery to lysosome and digestion
4. Release of particles into cytosol

Question 15

Describe the process of autophagy

Answer 15

1. Organelle surrounded by membrane
2. Delivery to lysosome
3. Recycling

Question 16

Describe how protein is sorted

Answer 16

Each protein has a unique sequence of amino acids that help with easy sorting:

1. Proteins are tagged
2. Proteins are sorted
3. Vesicles bud
4. Proteins interact with receptor (which are specific to the specific tag)
5. Delivery