---
tags:
  - biokemi
  - translation
  - instuderingsuppgifter
föreläsare: Ana Luis
---
## Genetic code

### Describe the main features of the genetic code.
```spoiler-block:
Triplet code (codons of three nucleotides), non-overlapping, read continuously, nearly universal, and unambiguous (each codon specifies one amino acid or stop).
```

### What is degeneracy of the genetic code and its biological significance?
```spoiler-block:
Multiple codons encode the same amino acid; this reduces the impact of point mutations and translation errors.
```

## Translation and tRNA

### What is translation?
```spoiler-block:
The process by which ribosomes synthesize proteins using mRNA as a template.
```

### What is a tRNA and what is its function in protein synthesis?
```spoiler-block:
A transfer RNA that carries a specific amino acid to the ribosome and matches it to the mRNA codon.
```

### What are the general characteristics of a tRNA?
```spoiler-block:
Small (~75 nt), cloverleaf secondary structure, L-shaped 3D structure, anticodon loop, and 3′-CCA end.
```

### Why is the 3′ CCA region called the acceptor arm?
```spoiler-block:
It is the site where the amino acid is covalently attached to the tRNA.
```

### What is the wobble effect and which base determines it?
```spoiler-block:
Flexible base pairing at the third codon position; determined by the first base (5′ end) of the anticodon.
```

### Why are aminoacyl-tRNA synthetases the ‘true readers’ of the genetic code?
```spoiler-block:
They ensure correct amino acid is attached to the correct tRNA, enforcing codon–amino acid fidelity.
```

### How do aminoacyl-tRNA synthetases work?
```spoiler-block:
Two-step reaction: amino acid activation with ATP, then transfer to tRNA; editing site removes mischarged amino acids.
```

## Ribosomes

### What is a ribosome and what are its components?
```spoiler-block:
A ribonucleoprotein complex of rRNA and proteins; composed of large and small subunits.
```

### Which ribosomal components are critical for structure and function?
```spoiler-block:
rRNA forms the structural core and catalyzes peptide bond formation.
```

### Describe the A, P, and E sites.
```spoiler-block:
A-site binds aminoacyl-tRNA; P-site holds peptidyl-tRNA; E-site releases empty tRNA.
```

### Differences between bacterial and eukaryotic ribosomes?
```spoiler-block:
Bacterial: 70S (30S+50S); eukaryotic: 80S (40S+60S).
```

### How can ribosomes be targets for antibiotics?
```spoiler-block:
Antibiotics selectively bind bacterial ribosomes, inhibiting translation without affecting eukaryotic ribosomes.
```

## Protein translation mechanism

### What are the steps of protein translation?
```spoiler-block:
Initiation, elongation, and termination.
```

### Characteristics of the bacterial initiation region?
```spoiler-block:
Shine–Dalgarno sequence upstream of start codon aligns mRNA with ribosome.
```

### Why is the reading frame established during initiation?
```spoiler-block:
Start codon positioning defines triplet grouping for the entire mRNA.
```

### How does protein initiation start and what is the role of initiation factors?
```spoiler-block:
Initiation factors assemble ribosomal subunits at the start codon and recruit initiator tRNA.
```

### Role of elongation and translocation factors?
```spoiler-block:
Deliver aa-tRNAs (EF-Tu/eEF1A) and move ribosome along mRNA (EF-G/eEF2).
```

### Role of release factors?
```spoiler-block:
Recognize stop codons and trigger peptide release.
```

### What is a polysome and its significance?
```spoiler-block:
Multiple ribosomes translating one mRNA simultaneously, increasing efficiency.
```

### Differences between bacterial and eukaryotic protein biosynthesis?
```spoiler-block:
Different ribosomes, initiation mechanisms, factors, and cellular localization.
```

### How does streptomycin inhibit protein biosynthesis?
```spoiler-block:
Binds 30S subunit, causes misreading of mRNA, and blocks initiation.
```