Genome organisation and replication Flashcards
What are the essential macromolecules in the continuity of life?
Nucleic acids
What does DNA stand for?
Deoxyribonucleic acid
What is the role of DNA in a cell?
Carries the genetic inheritance and instructions for the functioning of the cell
What does RNA stand for?
Ribonucleic acid
What is the role of RNA in a cell?
Communicates genetic information to the rest of the cell
What are the monomers that compose nucleic acids?
Nucleotides
What are the components of a nucleotide?
Nitrogen base + sugar phosphate backbone
What nucleotides compose DNA?
- Deoxyguanosine monophosphate (G)
- Deoxyadenosine monophosphate (A)
- Deoxythymidine monophosphate (T)
- Deoxycytidine monophosphate (C)
True or False: RNA is responsible for carrying genetic inheritance in a cell.
False
What are purines?
Two-carbon nitrogen ring bases
What are pyrimidines?
One-carbon nitrogen ring bases
Which bases are classified as purines?
Adenine and guanine
Which bases are classified as pyrimidines?
Cytosine and thymine
What are polynucleotide chains composed of?
Nitrogenous bases linked to a sugar-phosphate backbone
How are nucleotides linked in a DNA strand?
By phosphodiester bonds (C-O-P-O)
What gives the polarity of a DNA strand?
Phosphodiester bonds
What is the structure that the sequence of nucleotides is organized into?
Antiparallel double-helix
What two factors contribute to the stability of DNA double helix?
Hydrogen bonds between the bases of the opposite strands and base stacking of bases within a strand
What proteins pack DNA into tight shapes?
histones
What shape does packed DNA form?
chromatin
what is a nucleosome?
complexes of DNA and 8 histones
What are thr two types of chromatin conformation?
- open (euchromatin)
- closed (heterochromatin)
Why is chromatin remodelling important?
allows DNA to be exposed in the open conformation and accessed for replication, transcription and repair
what factors affect chromatin remodelling?
- Histone variants
- Histone post-translational modification
- ATP-dependent chromatin remodelling complexes.
How does semi-conservative replication work?
DNA replication accomplished by separation of the strands of a parental duplex, each strand then acting as a template for synthesis of a complementary strand.
The sequences of the daughter strands are determined by complementary base pairing with the separated parental strands.
in what direction does replication take place?
5’ to 3’
which proteins seperate DNA strands for access of DNA helicase?
initiator proteins
what does DNA helicase do?
breaks hydrogen bonds
what does primase do?
what does Topoisomerase do?
unwinds the DNA molecule
what does dNTP loose when it joins the DNA strand?
two phosphate groups as a molecule of pyrophosphate
what is the continuous strand in DNA synthesis called?
the leading strand
what is the discontinuous strand in DNA synthesis called?
the lagging strand
Why does DNA polymerase create problems for the linear DNA of eukaryotic chromosomes?
The replication machinery cannot complete the 5′ ends, leading to shorter and uneven DNA molecules after repeated replication.
Why is the limitation of no 5’ ends not a problem for prokaryotes?
Most prokaryotes have circular chromosomes, which do not have end-replication issues.
What are telomeres in eukaryotic chromosomal DNA?
telomeres are special nucleotide sequences at the ends of DNA molecules
What is the function of telomeres?
They do not prevent DNA shortening but postpone the erosion of genes near DNA ends
What is a mutation?
A mutation is an inherited alteration in the DNA sequence, which can be inherited within the same organism and across generations.
What causes mutations?
Mutations can be caused by replication errors or chemical damage to DNA
How does the cell address mutations?
DNA repair mechanisms exist to correct mutations.
what are the different types of DNA repair mechanisms?
- Base Excision Repair (BER) (Removes a single damaged base and replaces it)
- Nucleotide Excision Repair (NER) (Removes bulky lesions)
- Mismatch Repair (MMR) (Corrects errors made during DNA replication, such as mismatched bases or small insertions/deletions)
- Homologous Recombination (HR) (Repairs double-strand breaks (DSBs) using a homologous template (usually the sister chromatid).
- Non-Homologous End Joining (NHEJ) (Repairs double-strand breaks without a homologous template)
