Lecture 16 - Structure and Replication of DNA Flashcards
What is DNA? What are the three main components of its functional unit?
Deoxyribonucleic acid is a double-stranded, polypeptide molecule. It is made up of nucleotide molecules, each made up of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
A deoxyribose sugar have five carbons, each numbers in a particular order. To which end is the phosphate group connected to?
5’ end
Nitrogenous bases are categorized into two groups. What are they and mention its members.
Purine - Adenine and Guanine
Pyrimidine – Thymine and Cytosine
What are the pairs of nitrogenous bases?
A-T and G-C (3 hydrogen bonds)
Genes are mostly locate din chromosomes. Prokaryotic chromosome are found in _______. Eukaryotic chromosomes are found in the ________.
cytosol, nucleus
Chromosome consists of ______ and ______. Together, they form _______ which is the unfolded form of chromosomes.
DNA, protein (histones), chromatin
DNA is packaged with proteins called _____ to form the _______ (the basic unit of chromatin).
histones, nucleosome
(Extra) The _______ clamps the DNA double helix to a core of ___ histone molecules.
Histone H1, 8
Differ between euchromatin and heterochromatin in the context of epigenetic event.
Euchromatin is loosely coiled DNA that is transcriptionally active. Heterochromatin is tightly packed DNA that is transcriptionally inactive.
Methylation of promoters (epigenetic event) may convert euchromatin to heterochromatin.
DNA replication occurs during the _____ stage of the cell cycle.
Synthesis
DNA replication in eukaryotes and prokaryotes start at the _______.
Origin of Replication
Describe function of helicase.
separates strands of DNA (anti-parallel)
Once the DNA strand is separated, considering the unstable nature of ssDNA, which compounds help separate the strands apart?
the enzyme topoisomerase relieves supercoiling of single-stranded DNA, while single-stranded binding proteins keep the strands apart
Differ the function of DNA polymerase I and III.
DNA polymerase III is responsible for DNA replication by adding complement bases to the template (requiring a short double-stranded region to start).
DNA Polymerase I replaces RNA primers with DNA sequences.
DNA Polymerase III can only read DNA from ___ to ____. Hence, bases are added from the ____ to the ___.
3’ –> 5’ end
5’–>3’ end
Explain the concept of a leading and lagging strand.
The leading strand is the strand of DNA which is being synthesized in the same direction as the growing replication fork.
The lagging strand is the strand of DNA which is being synthesized in the opposite direction as the growing replication fork.
Short sequences forms on lagging strands are called ______.
Okazaki fragments
Differ between prokaryotic and eukaryotic replication.
Longer Okazaki fragments and faster rate of base addition in prokaryotes, eukaryotes have various types of DNA polymerase, eukaryotic DNA replication also involves the replication, disassembly, and assembly at the replication fork
Chromosomes require three elements to function. Mention all of them and explain.
Telomeres: structural stability, replication
Centromeres: essential for segregation during cell division
Origo: replication start point
What are telomeres? What are their importance in the context of DNA replication?
Telomeres are repeated sequence at the ends of chromosomes. It acts as a buffer to the degradation of functional gene sequence in the gene sequence by looping or recruiting protective protein.
How does degradation of chromosome occur? In which strand?
During lagging strand replication, sometimes there is a overhang, where there is not enough base sequence for primer placement and DNA replication. The overhang therefore is not replicated and is degraded.
How does telomerase lead to the concept of immortal cells?
Enzyme telomerase extends the lagging strand, allowing DNA polymerase to complete replication. This extension of the telomeres can occur indefinitely and in theory lead to immortal cells.
(Bonus) Explain how high levels of telomerase in cells may not be beneficial to an individual.
Damaged cells which normally would degrade faster would be repeated continuously, increasing risk in the error in the metabolic pathway.
Cancer cells have high levels of telomerase, allowing its capability of unlimited self-renewal.
