Bacterial RNA Translation to Proteins

translation

mRNA is converted to amino acid sequence

codons

triplets of nucleotides arranged in a sequence by messages in mRNA and represent individual amino acids

ribosomes

the machines that read the language of mRNA and translate it into protein

how do ribosomes read mRNA and translate it into protein?

via the genetic code

tRNA

decoder molecules that covert the language of RNA into that of proteins

what shape is tRNA in ?

a clover leaf shape

what are the two functional regions of tRNA?

anticodon and 3’ acceptor end

anticodon end of tRNA

hydrogen bonds with the mRNA codon specifying an amino acid

binds with the mRNA codon in an antiparallel fashion

3’ acceptor end of tRNA

binds to the amino acid

what do the two subunits of ribosomes inlude?

rRNA and proteins

what ribosomal subunits do prokaryotes have?

30S and 50S subunits and combine to form 70S ribosome

what does the 30S subunit contain?

16S rRNA

Carl Woese

used small subunit rDNA to construct tree of life

rDNA sequences also used to determine evolutionary distance among species

16S rRNA serves as a molecular clock for bacterial species

Shine-Dalgarno sequence

5’-AGGAGGU-3’

complementary to a sequence at the end of 16S rRNA subunit

what are the three stages of protein synthesis?

inititiation

elongation

termination

initiation of protein synthesis

brings the two ribosomal subunits together, placing the first amino acid in position

elongation in protein synthesis

sequentially adds amino acids as directed by mRNA transcripts

termination in protein synthesis

releases the completed protein when it encounters a stop codon

GTP

each phase of protein synthesis requires a number of protein factors in this form of energy

P site

where a tRNA carrying the first amino acid is paired with the start codon on the mRNA in initiation

A site

a second codon of the mRNA pairs with a tRNA carrying the second amino acid here

E site

the ribosome moves along the mRNA until the second tRNA is in the P site. the next codon to be translated is brought into the A site and the first tRNA is now here.

polycistronic mRNA

different ribosomes bind simultaneously to the start of each citron within this RNA

coupled transcription and translation

before RNA polymerase has even finished making an mRAN molecules, ribosomes will bind to the 5’ end of the mRNA and begin translating protein

why is coupling of transcription and translation impossible in eukaryotic cells?

they have a nuclear membrane that separates the two processes

post translational modification

1. after translation, proteins fold to their functional structure

2. if not made or folded correctly, proteins will get degraded

3. others get secreted using the protein traffic control

secretion: protein traffic control

proteins destined for the bacterial cell membrane or envelope regions require special export systems

N-terminal signal sequences

proteins for the cell membrane are tagged with this 15-30 hydrophobic amino acid sequence

signal recognition particle (SRP)

N-terminal signal sequences are bound by these

proteins then undergo cotranslational or posttrasnlational export

transmembrane proteins

some proteins designated for integral membrane location are inserted directly

transmembrane proteins SRP and FtsY

a ribosome paralyzed by SRP does not resume translating protein until encountering FtsY in the membrane

transmembrane proteins Sec system

other membrane proteins are inserted through here

protein export to the periplasm

periplasmic proteins are delivered to the periplasm by SecA-dependent general secretion pathway

SecB

keep protein unfolded

if it gets folded in cytoplasm then it will be stuck there

SecA

move proteins to SecYEG

SecYEG

exports proteins across the cell membranes of bacteria

example of Gram negative bacteria that need to export proteins completely out of the cell

digestive enzymes and toxins

seven elegant secretion systems have evolved

labeled Type I-VII

Type I secretion system

exports proteins to the outside environment

streptomycin

inhibits 70S ribosome function

tetracycline

inhibits translation by binding to 30S subunit

Chloramphenicol and Erthromycin

binds to 23S rRNA of the 50S ribosomal subunti