Genetics of Bacteria

Question 1

Components of Bacterial Cell Wall

Answer 1

Peptidoglycan cell wall; mucopeptides, mureins (strengthening material), glycoproteins

Question 2

Ribosomes in Bacteria

Answer 2

70S ribosomes; 50S and 30S subunits

Question 3

Function of Ribosomes in Bacteria

Answer 3

Sites of protein synthesis

Question 4

Plasma membranes in Bacteria

Answer 4

Phospholipid bilayer

Question 5

Function of Flagella in (Motile) Bacteria

singular: flagellum

Answer 5

Locomotion; rotate to propel bacteria forward

Question 6

Function of Pili in Bacteria

singular: pilus

Answer 6

Allow attachment to other cells

Question 7

Function of Capsules (Slime Layers) in Bacteria

Answer 7

• Protection against chemicals and dessication
• Store waste products
• Protect from attack by phagocytes

Question 8

Function of Photosynthetic Membranes in (Photoautotrophic) Bacteria

Answer 8

Tubular infoldings of plasma membrane; contain photosynthetic pigments

Question 9

Function of Mesosomes in Bacteria

Answer 9

foldings of plasma membrane; associate with DNA during cell division and help with formation of new cell walls, site of respiration

Question 10

Function of Fimbriae in Bacteria

Answer 10

Attachment to other cells or surfaces

Question 11

Function of Endospores in Bacteria

Answer 11

Survival structures in adverse conditions

Question 12

Describe structure of prokaryotic genomes.

Answer 12

• single copy of dsDNA (monoploid), located in nucleoid
• associated with non-histone proteins to form loop domains which subsequently supercoil to form condensed DNA
• may contain plasmids carrying genes not essential for survival, but may be important for growth and life cycle; genes in bacterial chromosome required to encode proteins essential for survival

Question 13

Outline asexual reproduction in bacteria by binary fission.

Answer 13

• bacterial chromosome must be replicated; replication begins at origin of replication (OriR) and occurs bidirectionally
• as DNA is circular with no free ends, interlocking structure consisting of 2 DNA molecules is formed; topoisomerase needed to cut, separate and reseal DNA molecules by breaking phosphodiester bonds
• duplicated DNA molecules attach to plasma membrane and cell elongates to prepare for cell division
• duplicated DNA then separate and plasma membrane invaginates to form septum; new cell wall layers form within membrane layers

Question 14

Advantages of binary fission

Answer 14

Advantageous in stable, favourable environment as it allows successful phenotypes to rapidly colonise a habitat and thrive

Question 15

Outline mechanism of transformation in prokaryotes.

Answer 15

• mode of gene transfer in bacteria in which a piece of free DNA is taken up from surrounding medium and integrated into bacterial chromosome
• DNA released into environment through cell death or other natural processes
• as DNA enters cell, one strand is hydrolysed by nucleases (DNAses) while other strand moves across plasma membrane of bacterium
• strand pairs up with homologous region of bacterial chromosome and is integrated through double crossover event; genetic recombination and homologous recombination occurs, forming transformant
• bacterial enzymes degrade remaining ssDNA
• transformed cell expresses genes received from DNA taken up, passing them on to offspring during binary fission

Question 16

Outline mechanism of generalised transduction in prokaryotes.

Answer 16

• process in which bacterial DNA is transferred from one bacterium to another by VIRULENT bacteriophages due to abberations in bacteriophage reproductive cycle
• bacteriophage infects bacterium; bacterial chromosome broken into random fragments
• sometimes, these random fragments are packaged into the capsids instead of phage DNA, forming transducing phages
• during cell lysis, transducing phages released and they can then inject host DNA instead of phage DNA into another bacterium
• integrated through double crossover event; genetic recombination and homologous recombination occur, producing transductant

Question 17

Outline mechanism of specialised transduction in prokaryotes.

Answer 17

• process in which TEMPERATE bacteriophages integrate their genomes as a prophage into bacterial chromosome
• occasionally, prophage may imprecisely excise from bacterial chromosome, carrying small part of bacterial DNA next to site of prophage integration
• this DNA may be packaged into capsid of phages; phages released during cell lysis and can then infect another bacterium
• DNA integrated through double crossover event; genetic recombination and homologous recombination occur

Question 18

Outline mechanism of conjugation in prokaryotes.

Answer 18

• unidirectional transfer of genetic material from F+ cell to F- cell
• F+ cell containing fertility factor produces sex pilus and cells are pulled together through cell-to-cell contact; cytoplasmic bridge forms avenue for DNA transfer
• endonuclease cleaves one strand of the F plasmid at the origin of transfer (OriT), allowing it to enter the F- cell in a 5’→3’ direction
• at the same time, nicked strand in F+ cell is replaced through rolling circle mechanism, producing double-stranded copy of the F plasmid
• whole F factor transferred; F- cell is now an F+ cell