The Diversity of Cells

Question 1

Where did monomers come from?

Answer 1

• Monomers came from space
• Monomers came from atmospheric reactions
• Monomers came from hydrothermal vents

Question 2

What did Stanley Miller and Harold Urey show in 1953?

Answer 2

Stanley Miller and Harold Urey showed in 1953 that the gases in the atmosphere could react to form small organic molecules (amino acids; fatty acids; organic acids). Rainfall would have washed those into the ocean forming an “organic soup” and leading to self-assembly into polymers and additional chemical reactions.

Question 3

How did the first cells form?

Answer 3

• Cells first formed in water

Lipids are amphiphilic. When they are mixed with water, they form micelles and vesicles with bilayers, trapping other organic molecules inside. Those that assembled to self-replicating units would constitute the first “proto-cells”. They came into existence in aquatic environments.

Question 4

Describe the basic cell structure.

Answer 4

All cells have certain structures in common:

1. Genetic material – in a Nucleoid or Nucleus
2. Cytoplasm – a semifluid matrix
3. Plasma membrane – a phospholipid bilayer

The membrane lipid bilayer contains
phosphoglycerides, glycolipids and can also
contain cholesterol (in animals) and sphingolipids.
The surface of the membrane is polar and contains
charged groups.

Question 5

What are the simplest cells?

Answer 5

The simplest cells are prokaryotes.

Question 6

When were cells first discovered?

Answer 6

Cells were discovered in 1665 by Robert Hooke.

Question 7

Describe Schwann’s Cell Theory

Answer 7

Schleiden and Schwann proposed the Cell Theory (1839):

1. All organisms are made of cells
2. Cells are the fundamental unit of life
3. Cells come from other cells

Question 8

What are some characteristics of bacteria?

Answer 8

Bacteria
•Cell membrane contains ester bonds
•Cell wall made of peptidoglycan
•React to antibiotics differently than Archaea
•May be Gram-positive or Gram-negative

Question 9

What are some characteristics of archaea?

Answer 9

Archaea
•Cell membrane contains ether linkages
•Cell wall lacks peptidoglycan
•Extremophiles-thrive in extreme conditions (high salt/temp)
•Genes and some metabolic pathways closely related to Eukaryotes (enzymes involved in transcription/translation)
•Most Archaea stain Gram-negative

Question 10

How did the first eukaryotic cells come into existence?

Answer 10

Eukaryotes evolved from prokaryotes

Question 11

Describe the endomembrane system

Answer 11

The endomembrane consists of a series of interconnected membranes in the cytoplasm:

1. The endoplasmic reticulum
2. The Golgi apparatus
3. Lysosomes

Question 12

Describe the rough endoplasmic reticulum

Answer 12

The rough ER is responsible for the synthesis of proteins with a signal
sequence. These proteins either remain in the ER, are sent to Golgi, lysosomes, vacuole, or plasma membrane, or are secreted. When misfolded/ unfolded proteins accumulate in the ER lumen due to stress, a mechanism known as the unfolded protein response (UPR) is activated. This triggers a reduction of protein synthesis and an increase in protein degradation. Failure in the response leads to apoptosis (programmed cell death).

Question 13

Describe the smooth endoplasmic reticulum

Answer 13

The smooth ER plays a role in the synthesis of lipids and steroid hormones, and in calcium storage.

Question 14

What is the Golgi apparatus?

Answer 14

The Golgi apparatus modifies, transports, and packages proteins and lipids for transport to their destination in the plasma membrane, lysosome, vacuole, or for secretion. In plants, it also produces cell wall polysaccharides.

Question 15

Describe lysosomes

Answer 15

Lysosomes are membrane-bound vesicles that break down macromolecules and foreign matter.

Question 16

Describe the evolution of the nucleus and the
endomembrane system

Answer 16

Question 17

Why would it be beneficial for an ancient eukaryote to engulf but not degrade an aerobic prokaryote?

Answer 17

The acquisition of aerobic bacteria would have provided a cell with the ability to carry out oxidative metabolism, and aerobic metabolism produces the most energy.

Question 18

Describe some details about mitochondria

Answer 18

Mitochondria occur in virtually all cells of animals, plants, and fungi

• They are surrounded by 2 membranes:

• smooth outer membrane
• folded inner membrane with layers called cristae
• They contain some of their own DNA; part of their genetic information is located in the nucleus
• Mitochondria are the location of ATP production through the citric acid cycle and oxidative phosphorylation.

Question 19

Describe the function of mitochondria-associated ER membranes (MAMs)

Answer 19

The MAM plays a role in lipid trafficking
and, possibly, Ca-signaling and the secretory pathway.

They are held together by protein-tethering complexes along with the mitochondria.

Question 20

What is the purpose of mitochondrial cristae?

Answer 20

Increase surface area of the mitochondrial inner membrane, thereby increasing the efficiency of energy production.

Question 21

How do cells modify mitochondria to lead to thermogenesis?

Answer 21

Uncoupling of proton transport from ATP production can lead to thermogenesis.

Question 22

Describe the Endosymbiosis Theory

Answer 22

The Endosymbiosis theory proposes that mitochondria and chloroplasts evolved from a symbiotic relationship. One prokaryote engulfed a second prokaryote and benefitted from its ability to, for example, photosynthesize. Over time, it lost its autonomy – some genes from the endosymbiont were transferred to the nucleus of the host.

Question 23

What is the evidence supporting the Endosymbiosis Theory?

Answer 23

1. Chloroplasts and mitochondria have 2 membranes: the outer membrane
   resembles the eukaryotic membrane; the inner membrane resembles the
   prokaryotic membrane
2. Possess DNA and ribosomes; the ribosome resemble prokaryotic ribosomes
3. About the size of a prokaryotic cell
4. Divide by a process similar to bacteria (binary fission)

Question 24

Why do we think mitochondria were first endocytosed?

Answer 24

Cells with chloroplasts also contain mitochondria, but not all cells with mitochondria contain chloroplasts.

Question 25

How are plants different from animals at a cellular level?

Answer 25

Plants have a large vacuole, cell wall, and more organelles.

Question 26

Describe the structure and function of Vacuoles

Answer 26

Vacuoles are membrane-bound structures within most plant and fungal cells. They can also be found in some protists (contractile vacuole) and animals.

In plants, they can serve similar functions as lysosomes in that they can also contain hydrolytic enzymes. However, they also serve as a storage organelle for ions (Ca) and proteins, contain nutrients and waste products, store metabolites (anthocyanin) to make the purple color in petals), they participate in cell expansion and maintain the turgor pressure in the cell.