otro2

Question 2

Where does translation start in prokaryotes and eukaryotes? Describe the process.

Answer 2

The ribosome attaches its two units to the
mRNA and begins to read it from the 5’ to the 3’ end until it reaches the start codon ( AUG,GUG,UUG) ( AUG Met)
The start codon is preceded by a whole initiation complex , in the middle of which is a purine-rich sequence :
ÿ Prokaryotes: Shine-Dalgarno sequence
ÿ Eukaryotes: Kozak sequence

Question 3

Name at least two antibiotics and/or toxins that inhibit protein synthesis and briefly describe the mechanism.

Answer 3

Streptomycin: inhibits initiation (inhibits binding of fMet-rTRNA) and thus causes a
incorrect reading of mRNA
Tetracycline: binds to the 30 subunit and inhibits the attachment of the aminoacyl-tRNA

Question 4

What is the typical structure of eukaryotic transcription factors? Name three typical DNA binding structures.

Answer 4

Transcription factors bind to specific sections of DNA and regulate how much messenger RNA (mRNA) is produced
from it (transcription rate).
1.DNA-binding domain:
2.Activation domain: initiates transcription through interactions with RNA Pol II and/or its associated proteins or
through local changes in chromatin structure
DNA-binding structures in eukaryotic transcription factors:
-* Homeodomain (helix-turn-helix)
* Leucine zipper domain (bZip domain)
* Zinc finger domains

Question 5

The binding of oxygen depends on the oxygen partial pressure:

Answer 5

• high O2 partial pressure: protein is oxygenated > R-form
• low O2 partial pressure, no O2 bound > T-shape

Question 5

e Bohr effect

Answer 5

describes the decrease in the affinity of hemoglobin (Hb) to oxygen when the pH value decreases
or the CO2 concentration increasesThe lower the pH value, the easier H+ is absorbed and O2 is released.

Question 6

Types of enzyme regulation: Explain how the enzymatic activity of proteins can be regulated. Give one
example of each.

Answer 6

1. Allosterische Regulation - Aspartat Transcarbamoylase
   Activator molecules occupy the allosteric center and thus cause a conformational
   change:
2. Regulation with Isoenzyme - LDH-Formen: M4-Isoenzym, H4-Isoenzym
3. Regulation by covalent modification - histones in DNA packaging
4. Activation by proteolytic cleavage - pepsin in the stomach, trypsin in the pancreas
5. Activation by co-activators – CoA, metal ions