The Eukaryotic Cell

Question 1

What are the 3 ‘super kingdoms’ in the classification system?

Answer 1

Bacteria, archaea, and eukarya.

Question 2

What are the 6 kingdoms in the classification system?

Answer 2

Bacteria, Archaea, Protista, Plantae, Fungi, Animalia

Question 3

Describe 3 features of the first atmosphere on Earth.

Answer 3

• very little oxygen
• rich in water vapour
• rich in compounds released from volcanic eruption (e.g CO2, nitrous oxides, methane, ammonia, hydrogen)

Question 4

What is the most compelling theory describing how life evolved on Earth initially?

Answer 4

• Life evolved at hydrothermal vents located at bottom of ocean floor
• seawater mixing with rock from earths mantle created chemistry that enabled formation of amino acids and nucleotides.

Question 5

First life on earth was in the form of what organism?

Answer 5

Prokaryotic chemotrophs

Question 6

Describe the great oxidation event and what it was critical for.

Answer 6

• photosynthetic prokaryotes produced oxygen

- critical to the evolution of aerobic organisms

Question 7

When do eukaryotic cells first appear in the fossil record?

Answer 7

1.8 billion years ago.

Question 8

What were the first eukaryotic fossils?

Answer 8

Precambrian acritarch fossils.

Question 9

Where do scientists believe early eukaryotes lived?

Answer 9

In the water column, freely suspended

Question 10

List the 3 earliest eukaryotes and when they appeared in the fossil record chronologically.

Answer 10

1.4 billion years ago - Grypannia
(Filamentous green algae spiral thingy)

635 million years ago - early Seaweed

500 million years ago - Burgess Shale animals (Cambrian)

Question 11

Compare prokaryotes and eukaryotes in terms of:

• presence of mitochondria
• DNA shape
• histone proteins with DNA
• nuclear envelope and endoplasmic reticulum

Answer 11

• only eukaryotes have mitochondria
• prokaryotes have circular DNA, eukaryotes linear DNA
• only some proks have histones, all euks have histones
• only euks have nuclear envelope and ER

Question 12

Compare prokaryotes and eukaryotes in terms of:

• multicellular or uni
• cell size
• genome size
• gene number
• meiosis (sexual or asexual)

Answer 12

• proks are unicellular, euks are multicellular
• prokaryotes are <10 micrometers, euks are 3 micrometers to 10 mm
• proks have very little bases, euks have way more bases
• proks have ~4000 genes, euks have 6000-35000 genes
• proks are asexual, euks undergo meiosis (sexual)

Question 13

What archaeal group are eukaryotes most closely related to?

Answer 13

Lokiarchaeota

Question 14

What 2 features are characteristic of Lokiarchaea?

Answer 14

• actin homologise in cytoskeleton

- vesicular trafficking machinery

Question 15

The acquisition of WHAT was key in the evolution of eukaryotes and why?

Answer 15

Mitochondria, gave eukaryotes power

Question 16

What did eukaryotes evolve from?

Answer 16

Prokaryotes

Question 17

Describe two key features of the most recent ancestor of eukaryotes and archaea.

Answer 17

• cytoskeleton

- endocytosis and/or phagocytosis

Question 18

List 3 features of the most recent common ancestor of eukaryotes.

Answer 18

• nucleus
• mitochondrion
• membrane bound organelles

Question 19

What are the two main theories describing how eukaryotes might have acquired the mitochondria?

Answer 19

Endosymbiosis: outside in model
Eukaryote host engulfed a purple bacterium

Endosymbiosis: inside out model
Eukaryotes and purple bacterium initially had close symbiotic relationship, over time projections of cell wall from eukaryote slowly enveloped purple bacteria.

Question 20

List 7 key features that are evidence of how eukaryotes increased their genome size and complexity.

Answer 20

• nuclear envelope and endoplasmic reticulum
• linear chromosomes
• multiple chromosomes
• telomeres
• multiple replication origin points
• histone proteins
• gene duplication

Question 21

What is the old and now inaccurate theory of how the endomembrane system evolved in eukaryotes?

Answer 21

• invagination (folding in) of plasma membrane to create nuclear membrane and endoplasmic reticulum

Question 22

Describe the new and more accepted theory of how the endomembrane system evolved. What is the evidence for this?

Answer 22

• mitochondria was already in ancestral eukaryotes before the endomembrane system evolved
• bacteria secrete outer membrane vesicles containing lipids for signaling and these are the same as mitochondrial vesicles
• vesicles from the mitochondria might have fused together to generate membrane structure that evolved into the endomembrane system.

EVIDENCE: eukaryotic plasma membrane has lipid composition more similar to bacteria than ancestral archaea

Question 23

Describe the origin of the nuclear envelope.

Answer 23

• during nuclear division, envelope disintegrates
• chromosomes divide and separate
• ER clusters around chromosomes and forms new envelope

Question 24

How many chromosomes do prokaryotes have?

Answer 24

1 circular chromosome

Question 25

How are eukaryotes able to contain so much more DNA?

Answer 25

Bc of histones and their packaging mechanism.

Question 26

Describe the steps of how a new bacterium is made.

Answer 26

1. Circular chromosome is attached to cell membrane at specific point 2. DNA replicates the cell grows 3. The two copies of DNA are separated by expansion of the cell membrane between the attachment points. 4. Membrane furrows inwards to divide cell in two.

Question 27

Describe a selection pressure for why bacteria have so few genes.

Answer 27

- bacterial chromosomes have a single replication origin - more genes requires more time to replicate - bacteria would therefore get out-competed by faster replicating organisms

Question 28

Why don’t bacterial chromosomes have multiple origin points?

Answer 28

More than one origin requires multiple decatenation points, too complicated (Russian wedding ring problem) Impossible for two chromosomes to untangle as lots of bits of DNA would be linked together

Question 29

Do linear eukaryotic chromosomes have catenation (linking of strands)? Explain why.

Answer 29

No, because they are linear and have multiple replication origins.

Question 30

What is an advantage of the evolution of linear chromosomes?

Answer 30

- longer piece of DNA with multiple origin points, manageable replication/generation time - multiple chromosomes to increase DNA content and complexity

Question 31

What is a disadvantage of linear chromosomes?

Answer 31

- a small amount of DNA at the end of chromosomes is lost with every replication (DNA with RNA primer attached is unreplicated so it degrades) - linear chromosomes therefore less stable than circular chromosomes because of the end problem

Question 32

How do telomeres solve the end problem of linear eukaryotic chromosomes?

Answer 32

- keep adding sacrificial non coding DNA that the RNA primer can attach to and later delete without losing cruciak genes

Question 33

What did Fukui Ishikawas experiment involving fission yeast show about telomeres?

Answer 33

Fission yeast is eukaryotic, once genes for telomere formation were deleted, yeast nearly all died. Therefore couldn’t survive with linear chromosomes because they just got shorter and shorter When they made the chromosomes circular, they could grow ok and divide by binary fission but unable to have sexual reproduction

Question 34

What is parasitic/junk DNA?

Answer 34

Introns (non coding parts of DNA) that interrupts the DNA words in a gene. Still transcribed into mRNA, but is excised before translation.

Question 35

What key processes does the nuclear envelope of the nucleus separate? Why is this important?

Answer 35

- nucleus separates transcription and translation - acts as barrier to prevent precocious translation that would make a dodgy protein if introns are still present - ensures intron excision prior to translation

Question 36

Since prokaryotes don’t have a nucleus, would they survive having introns in their genes? Why or why not?

Answer 36

No because without nucleus, transcription and translation are coupled. No time to excise introns. Therefore would not survive bc too many defunct proteins produced if introns present!

Question 37

What are the two theories about the origin of the evolution of meiosis? Which one is said to be more accurate?

Answer 37

1. From mitosis (too many changes from mitosis) | 2. From bacterial transformation (more accurate)