DNA and RNA Flashcards
(18 cards)
Explain the structure of DNA
Double Helix
Anti-parallel
strands joined by non-covalent (phosphodiester) bonds
made of many nucleotides joined
nucleotides:
- 5 carbon sugar (penrose)
- 1’ carbon: nucleobase
- 5’ carbon: phosphate group (negative charge)
explain DNA polymerization reaction
phosphodiester bond formation
condensation reaction which releases small stable molecule
releases pyrophosphate (PPi) and proton (H+)
happens in 5’ to 3’ direction !
5’ phosphate group of 1 links to 3’ hydroxyl group of another
explain the differences between nucleobase, nucleoside and nucleotide
base: nitrogenous base: adenine, guanine, cytosine, uraxil, thymine
nucleoside: base + pentose: adenosine, guanosine, cytidine, uridine, deoxythymidine
nucleotide: nucleoside + phosphate
mono, di, or triphosphate
AMP, ADP, ATP
adenosine monophosphate
guanosine monophosphate
cytidine monophosphate
uridine monophosphate
deoxythymidine monophosphate
explain in simple terms the steps of DNA replication
- Helicase unwinds dsDNA by breaking hydrogen bonds to form a replication bubble
- the junction of the unwound molecules is a replication fork and is extended bidirectionally
- single stranded DNA binding proteins join near the form to prevent unwound strands from rejoining
- topoisomerase joins and prevents supercooling of DNA as strands unwind
- primase synthesizes a short RNA primer in the replication bubble
- DNA polymerase 3 binds to primer and synthesizes daughter strands from parental strands - a new strand is formed by pairing complementary bases with the old strand (template)
- in the lagging strand primers are continuously made and DNA polymerase jumps to primers and extends them
- DNA ligase joins the Okazaki fragments together to form the lagging strand (phosphodiester bond formation) 9. 2 molecules are made - each has one new and one old DNA strand
why is DNA replication considered semi-conservative
each daughter strand has 1 parental strand and 1 newly synthesised strand
what directions is DNA read in and synthesised in
polymerase reads in 3’ to 5’ direction
synthesized 5’ to 3’ direction (direction of replication fork)
explain continuous vs discontinuous replication
continuous: strand of DNA 3’ to 5’ and is called the leading strand, synthesis can happen continuously 5’ to 3’ direction antiparallel
discontinuous: strand 5’ to 3’, therefore read in short okazaki fragments in 5’ to 3’ direction
which enzymes are involved in DNA replication and explain their functions
- Helicase: unwinds dsDNA by breaking hydrogen bonds between 2 strands
- single-stranded DNA binding proteins: binds single-stranded DNA preventing unwound strands from joining
- Topoisomerase: prevents supercoiling of DNA as strands unwind - does this by breaking and reforming DNA phosphate backbone ahead of replication fork to relieve pressure
- Primase: synthesizes a short RNA primer required for DNA polymerisation
- DNA polymerase: synthesizes daughter strands from parental strands (5’ to 3’ direction) - phosphodiester bond formation
- DNA ligase: joins/ligates Okazaki fragments together to form the lagging strand primers- phosphodiester bond formation
what is responsible for DNA synthesis proofreading
exonuclease activity - a function of the DNA polymerase
how does the proofreading process of DNA synthesis work
the exonuclease activity works in a 3’-5’ direction
if the incorrect nucleotide is added to the extension of the primer, the DNA polymerase stalls and cannot add the next nucleotide to the chain
stalling allows for the proofreading activity of the exonuclease to remove the incorrect base
this activity is slow compared to polymerising activity
what are the characteristics of DNA replication
semi-conservative
bi-directional
semi-discontinuous
what is the central dogma of molecular biology
a theory that states that genetic information flows in one direction only, either from DNA to RNA to protein (replication + transcription + translation) or from RNA to protein (translation)
explain the structure of RNA
= a polymer of purine or pyrimidine ribonucleotides linked by 3’-5’ phosphodiester bridges
- bases are either purine (Pure As Gold - adenine & guanine - double ring) or pyrimidine (Cut the pie - cytosine & adenine & uracil - single ring)
single stranded, shorter & can be hydrolysed by alkali due to the OH group on 2’ carbon
ribose sugar
uracil instead of thymine
what is transcription briefly
synthesis of RNA
what are the differences btwn transcription and DNA replication
no primer required in transcription
only small portion of genome is transcribed in transcription
what is required for transcription to take place
- DNA
- Ribonucleotides (ATP, CTP, UTP, GTP)
- RNA polymerase which needs MG2+
why does RNA polymerase require Mg2+
- Helps Add Nucleotides – Mg²⁺ makes it easier for RNA polymerase to attach new RNA letters (nucleotides) by stabilizing them.
- Keeps the Enzyme in Shape – It helps RNA polymerase stay in the right form to work properly.
- Helps Remove Waste – When RNA is made, leftover pieces (pyrophosphate) need to be cleared, and Mg²⁺ helps with that.
explain the following terms and their roles in transcription: DNA coding/sense strand, DNA template/antisense strand, primary RNA transcript
DNA coding/sense strand (5’-3’): same sequence as RNA transcript, except RNA has U, sense has T. contains actual genetic code.
DNA template/antisense strand (3’-5’): used as template for RNA synthesis, RNA polymerase reads strand 3’-5’ and builds transcript 5’-3’. complementary to RNA transcript & sense
RNA transcript (5’-3’): newly made. in eukaryotes, pre-mRNA undergoes processing.
