2.Nuclear Acids

Question 1

(Closed-)Circular DNA

Answer 1

• in bacteria (prokaryotes) as plasmids or in eukaryotic cells (mitochondria, chloroplasts — having prokaryotic DNA)
• two complementary strands, each joined/linked into circles -> no free ends
  (Number of links know as linking number)

Supercoiling: coiling of DNA axis around itself (
- DNA mostly negatively supercoiled, means helix is untwisted -> fascilitate processes that require undwinding of helix like transcription or replication

Topoisomer:
- circular DNA-molecule with specific value of linking numbers which may not changed without first breaking one or both strands

Question 2

Linear DNA

Answer 2

• in eukaryotes
• can be single- or double stranded
• has free ends

Question 3

DNA functions

Answer 3

1. Stores an organism’s genetic information
2. Coding/Binding — all cellular proteins (histones, proteins in kinetic horse and mitosis spindle) which regulate gene activity
3. Regulatory — control gene activity through regulatory genes and production of proteins
4. Enzymatic — desoxyribozymes with nuclease activity

Question 4

Mitochondrial DNA

Answer 4

• a circular DNA (unique sequences only, 2-10 copies/cell), double stranded
• contains triple stranded regions (block replication and transcription)
• does not contain introns
• is not bound to histones
• autonomous (selbstbestimmende) replication and transcription
• specific genetic code (some genes don’t have terminating codons)
• maternal inheritance –> sperm mtDNA is degraded, children from both genders inherit diseases
• lack of repair mechanisms and proofreading capabilities ->high mutation
  rates