Lecture 12 - Ribosomes, etc.

Question 1

Major structures in the cytoplasm of prokaryotes

Answer 1

• nucleoid (containing DNA), ribosomes, and reserve deposits called inclusion bodies
• research also shows that bacteria also possess protein cytoskeleton components, some being homologous to euk proteins

Question 2

Cytoplasm

Answer 2

• approx. 70% wet weight of cell (mainly water)

- gel-like suspension of proteins (20%), ions, organics, ribosomes, nucleoid region with nucleic acids, gases, etc.

Question 3

Numbers for Prokaryotic Ribosome

Answer 3

First off ribosomes make up to 15-20% of cell mass.

• complete ribosome 70S
• 50S large subunit - 31 proteins, 2 rRNA molecules (5S and 23S)
• 30S small subunit - 21 proteins, 16S rRNA

Question 4

Large subunit involved in

Answer 4

Peptide bond formation through peptidyl transferase activity

• GTP aids in initiation, elongation, and termination
• 5S portion = stability

Question 5

Small subunit

Answer 5

decoding mRNA by providing the A, P, and E binding sites and by being responsible for base pairing between the codon on mRNA and the anticodon of tRNA

Question 6

Eukaryotic ribosomes

Answer 6

same function as prokaryotic, but ribosomes are larger

80S complete ribosome - 60s large subunit and 40S small subunit

Question 7

S - in measuring ribosomes stands for

Answer 7

unit rate of sediment (Svedberg units)

Question 8

Importance of knowing the structure of a ribosome…

Answer 8

We can target it! Antibiotic sits down on ribosome and blocks translation. ex. Z-pack (interferes with protein synthesis)

Question 9

Ribosomes envolved in…

Answer 9

Translation - formation of proteins

Question 10

Chromosome(s)

Answer 10

DNA - Large double stranded molecule organized into genes. It aggregates in the cell to form a mass visible by EM, called the nucleoid

• packed in loops back and forth
• nucleoid usually contains a single, long, continuous, and frequently circularly arranged thread of double stranded DNA (the bacterial chromosome)

Question 11

The chromosome is attached to the __________ . And DNA is _________ and is stabilized by interactions with proteins.

Answer 11

cell membrane

supercoiled

Question 12

One complete copy of the genetic information in an organism

Answer 12

genome

Although most have one large continuous double strand of DNA, some proks have multiple chromosomes, or even liner chromosomes.

Question 13

In a bacterial cell, the DNA is organized in loops called ________

Answer 13

domains

-in between the chromosome is condensed into approximately 500 loops

Question 14

The central point is the _________ .

At the opposite end is the _________.

Answer 14

• origin of replication, which is attached to the cell envelope at a point on the cell’s equator, halfway between two poles
• terminus

Question 15

Theta replication

Answer 15

at the origin, the DNA double helix is melted open by binding proteins, and then DNA polymerase synthesizes new strands in both directions (bidirectionally).

Question 16

Extra-chromosomal element in Proks

Answer 16

Plasmids (5-100 genes)

Question 17

Plasmids

Answer 17

• Often small, often circular ds DNA molecules
• autonomous replication
• single or multiple copies
• encode non-essential genes
• confer various capabilities like antibiotic resistance, degradative pathways, conjugation, tolerance to heavy toxic metals

Question 18

Borrelia burgdorferi (lyme disease)

Answer 18

1 chromosome, 12 linear plasmids, 9 circular plasmids