Prokaryotes & Eukaryotes

Question 1

Describe the cell structure and molecular biology of Prokaryotes

Answer 1

Cell structure:

no nucleus or double membraned organelles
Circular chromosomes
usually have rotating flagellum powered by PMF in bacteria and ATP in archaea (only example of true wheel in nature)
Cell division by fission
No chromosomes condensing
No motor proteins so cytoplasm isn’t as stern, no cytoplasmic streaming

Small - diffusion limited

MOLECULAR BIOLOGY
Not much junk dna
DNA lacks histone s - instead lightly packaged by proteins
RNAP use a sigma σ factor to initiate transcription

In BACTERIA, initiator tRNA used as start codon = tRNA formal methionine
- ribosomes are 70s- small s unit = Svedberg unit (measurement of size in relation to centrifugation)

Question 2

Describe the cell structure and molecular biology of Eukaryotes

Answer 2

CELL STRUCTURE

• nucleus
• multiple linear chromosomes
• endomembrane system
• endosymbiosis (plastids)
• cytoskeleton - not homologous to prokaryotes
• 9+2 microtubule structure (flagella/cilia)
• cell division by mitosis
• cytoplasm contains many large fibrillation proteins - not diffusion limited

MOLECULAR BIO

• genomes contain junk
• 3.2 Gbp in haploid form
• difficult to identify functional regulatory regions and mRNA
• DNA bound to nucleosomes by histones
• RNAP use TBP (tata binding protein) to find promoter of gene and initiate transcription
• tRNA methionine - start codon
• large 80s ribosomes

Question 3

Explain the evolutionary relationships between the three domains of life

Answer 3

Woese proposed 3 domains of Life based on rDNA sequences
- rDNA = ribosomal DNA - highly conserved and essential
Eubacteria and archaea = paraphyletic group
Eukaryota = monophyletic group
- can be sister group
- or paraphyletic w.r.t archaea

Question 4

Describe the cell structure and molecular biology of Archaea

Answer 4

Archaea has prokaryotic cell structure: no nucleus, no endosymbionts or cytoskeleton

Has eukaryotic molecular biology: histone bound DNA, tRNA methionine = start codon, RNAP use TBP

Question 5

Describe Margulis’s theory and whether archaea are more closely related to bacteria or eukaryotes

Answer 5

Mitochondria - proteobaxteria
Plastids - Cyanobacteria
Evidence - DNA inside, use 70s ribosomes, tRNA formalmet

Seems simplistic but horizontal gene transfer makes things messy

Gene transfer from endosymbiont to host makes it difficult to say if archaea are more closely related to eukaryotes than either are to bacteria.

Depends on genes looked at:
If information processing genes - show that eukaryotes and archaea are more closely related to each other

If metabolism genes - archaea and bacteria are more closely related to each other

Question 6

What is the Central Dogma according to Crick and Watson?

Answer 6

According to FRANCIS CRICK: proteins cannot go back to nucleus acids. Once ‘information’ has passed into a protein, it cannot get out again.

The transfer of info from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible

Prions = misfolded proteins with the ability to transmit their misfolded shape onto normal variants of same protein

Question 7

Give a brief overview of DNA to RNA To promoter

Answer 7

DNA contains 5’ flank where promoter region is located, transcribed region and 3’ flank where terminator is located
RNA polymerase (RNAP) binds to promoter

Transcribed region is transcribed into mRNA containing 5’ UTR (untranslated region) which has ribosome binding region, stop codon and 3’ UTR

tRNA with complementary anti codon to codon on mRNA binds to template strand and brings correct amino acid, eventually producing a protein