Topic 2.3 Nucleotides & Nucleic acids Flashcards
What is the function of DNA and RNA together?
DNA holds genetic information, RNA then transfers this information to from DNA to ribosomes made of RNA, and proteins
What is the full name for DNA
Deoxyribonucleic acid
What is the full name for RNA
Ribonucleic acid
What do nucleotides consist of
A pentose sugar
A nitrogenous base
A phosphate group
What are the components of a DNA nucleotides
- Deoxyribose
- A phosphate group
- One of the organic bases: adenine, cytosine, guanine, thymine.
What are the components of a RNA nucleotide?
- Ribose
- Phosphate group
- One of the organic bases: adenine, cytosine, guanine, uracil
What is the difference between a ribose and a deoxyribose?
A ribose has a hydroxyl group at the 2’ carbon whereas, a deoxyribose lacks the hydroxyl group ad has only one hydrogen at the 2’ carbon.
Explain the structure and function of a nitrogenous base.
The nitrogenous base is attached to the 1’ carbon of the pentose sugar via a glycosidic bond.
The base determines the identity of the nucleotide.
What is the meaning of a purine and which bases are part of it?
Purines are double-ring structures - larger molecules.
Adenine (A)
Guanine (G)
What is the meaning of a pyrimidine, and which bases are examples of it?
Pyrimidines are single-ring structure - smaller molecules.
Cytosine (C)
Thymine (T) in DNA
Uracil (U) in RNA
How does the synthesis of polynucleotides occur?
- through a condensation reaction
- phosphodiester bond is formed between the 3’ hydroxyl group of one nucleotides pentose sugar and the 5’ phosphate group of another nucleotide.
- this creates a sugar-phosphate backbone.
- during the reaction, water is released as a by-product.
How does the breakdown of a polynucleotide occur.
- breakdown occurs through a condensation reaction
- molecule of water is used to break the phosphodiester bond
- results in the release of individual nucleotides
List the reasons breakdown is necessary for:
- DNA repair mechanisms
- Recycling of nucleotides for new nucleic acid synthesis
- Controlled degradation of RNA after its function is complete.
What is ATP and ADP?
Adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are phosphorylated nucleotides essential for cellular transfer.
What are the components of ATP?
- Pentose sugar - ribose
- Nitrogenous base - adenine
- Three phosphate groups
What are the components of ADP?
- Pentose - sugar
- Nitrogenous base - adenine
- Two phosphate groups
What is the role of ATP in energy transfer within cells?
Energy is released when ATP is hydrolysed to form ADP and a phosphate molecule. This process is catalysed by ATP hydrolase.
The inorganic phosphate can be used to phosphorylate other compounds, as a result making them more reactive.
Condensation of ADP and inorganic phosphate, catalysed by ATP synthase, produces ATP during photosynthesis and respiration.
What are the properties of ATP:
- Small - movies easily into and out of and within cells
- Water soluble - energy-requiring processes happen in aqueous environments.
- Contains bonds between phosphates with intermediate energy: Large enough to be useful for cellular respirations but not so large that energy is wasted as heat.
- Easily regenerated - can be recharged with energy
- Releases energy in small quantities - quantities are suitable to most cellular need, so energy is not wasted.
What are the key components of DNA:
- Nucleotides
- Antiparallel strands
What are the complimentary base pairs held together by hydrogen bonding
- Adenine pairs with Thymine via two hydrogen bonds
- Guanine pairs with Cytosine via three hydrogen pairs.
Explain the importance of hydrogen bonds in the DNA
The hydrogen bonds provide stability to the DNA structure while allowing the strands to separate during processes like replication and translation.
Explain the formation of the double helix.
Two polynucleotide strands twist around each other to form the characteristic double-helix shape.
The shape is then stabilised by hydrogen bonding between base pairs.
Explain the process of Semi-conservative DNA replication.
The double helix unwinds and hydrogen bonds between base pairs break due to DNA helicase. This separates the two strands of DNA.
Both strands are used as templates and the complementary base pairing occurs between templates and free nucleotides.
Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase
What is the importance of semi-conservation DNA replication
It ensures genetic continuity between generations of cells meaning that genetic information is passed from one generation to the next.
What is the genetic code?
The genetic code is the set of rules by which the sequence of nucleotides in DNA is translated into the sequence of amino acids in a polynucleotide.
Explain the meaning of Triplet code:
Each amino acid is encoded by a sequence of three nucleotides, which are called codons, in the mRNA. Each codon corresponds to one specific amino acid in the resulting polypeptide chain.
Explain the how the genetic code is non-overlapping
The codons are read in a sequence without over-lapping. This means that each nucleotide is part of only one codon. The reading frame does not shift after each nucleotide.
Explain how the genetic code is degenerate
Some amino acids are encoded by more than one codon. There are 64 possible codons, but only 20 amino acids. The redundancy in the code means that multiple codons can specify the same amino acid.
Explain how the genetic code is universal
The same codons generally specify the same amino acid in
nearly all organisms, from bacteria to humans.
Explain Transcription during Protein Synthesis.
During transcription, a molecule of mRNA is made in the nucleus:
- The hydrogen bonds between the complementary bases break and the DNA uncoils thus separating the two strands.
- One of the DNA strands is used as a template by RNA polymerase to make the mRNA molecule. The DNA template is called the antisense strand.
- Free nucleotides line up by complementary base pairing and adjacent nucleotides are joined by phosphodiester bonds made by RNA polymerase thus forming a single stranded molecule of mRNA.
- mRNA then moves out of the nucleus through a pore and attaches itself to a ribosome in the cytoplasm, this is the next stage of protein synthesis called translation.
Explain Translation during Protein Synthesis.
During translation amino acids join together to form a polypeptide chain.
- mRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule with a binding site at one end, so it can only carry one type of amino acid, and a triplet of bases at the other.
- tRNA attaches itself to mRNA by complementary base pairing- two molecules attach to mRNA at a time.
- The amino acids attached to the two tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind.
- This process is repeated, therefore leading to the formation of a polypeptide chain until a stop codon is reached on the mRNA and ends the process of protein synthesis.
