DNA and RNA (A1.2.1, A1.2.6, A1.2.2, A1.2.3, A1.2.5, A1.2.7)

• What are the two main functions of nucleic acids?

  To pass information between generations

  To code for protein synthesis
• What are the two types of nucleic acid, and what are their main functions?

  There are also two types of nucleic acids:

  DNA- deoxyribonucleic acid

  DNA passes hereditary information between generations of cells.

  DNA codes for making RNA during transcription

  RNA- ribonucleic acid

  RNA codes for making proteins during translation

  mRNA, rRNA and tRNA are the three types of RNA used in protein synthesis

  They are both polymers with a sugar-phosphate backbone, but while DNA contains a deoxyribose, RNA contains a ribose.
• What does it mean that DNA and the genetic code are universal?

  DNA is universal to life. All living organisms use DNA as genetic material.

  The use of the genetic code across all forms of life as evidence of universal common ancestry of life. The sequences of DNA in cells can be analysed and compared to determine evolutionary relationships between organisms- the more similar the sequence, the more closely related the organism.

  Universal Code - All living organisms (bacteria, plants, animals, etc.) use DNA, showing a common evolutionary origin.

  Mutations Lead to Evolution - Changes in DNA can result in genetic variation, driving natural selection and evolution.

  Genetic Engineering - Since DNA is universal, scientists can manipulate it (e.g., GMOs, gene therapy).
• What is the structure of DNA?

  DNA is a polymer of nucleotides, with one of four different nitrogenous bases (ATCG). Each strand of DNA has a backbone of sugar-phosphates. The ends of the backbone are identified as 5' phosphate and 3' pentose.
• How is DNA formed?

  The DNA backbone is formed when nucleotides combine in a condensation reaction- the monomer nucleotides combine to form the polymer DNA chain, releasing water.

  In the condensation reaction that forms DNA, the 5' phosphate group on one nucleotide forms a new covalent bond (phosphodiester bond) with the 3' carbon on the deoxyribose of the next nucleotide. This forms the sugar-phosphate backbone. Therefore, during replication, DNA is built from 5' to 3'.

  Two backbones are held together by hydrogen bonds between the nitrogenous bases, to create the double-helix structure of DNA. This means that it has two strands, which wind around one another. The two strands run in opposite directions, so at each end of the double helix, one strand is 5', and the other is 3'. This means that the strands are antiparallel- which has implications for DNA replication and transcription.

  Hydrogen bonding between the nitrogenous bases is what holds the two DNA strands together in their anti-parallel double helix structure. Bases pair up through complimentary base pairing- AT GC
• What are nucleotides composed of?

  Nucleotides are composed of:

  A nitrogenous base Adenine (A) Thymine (T) Cytosine (C) Guanine (G) (Uracil (U)) The type and sequence of nitrogenous bases in the nucleic acid polymer forms the basis of genetic code.

  A five-carbon (pentose) sugar (either ribose or deoxyribose) The base and the phosphate group are connected to the carbon in the pentose via a covalent bond

  A negatively charged, acidic, phosphate group The negative charge allows DNA to be attracted to histones in nucleosomes, which allows DNA to supercoil
• What are pentoses?


  Pentoses are a type of monosaccharide, containing five carbons. They appear in the form of four carbons covalently bonded, plus an oxygen, forming a ring in the shape of a pentagon. Carbon 5 branches out of the ring. Two kinds of pentoses are ribose and deoxyribose.

  The carbons in the ring are labelled from 1- 4, moving clockwise starting with carbon 1 closest to the oxygen. It is the orientation of carbon atoms that determines the directionality of RNA and DNA, with implications for replication, transcription and translation.

  The difference between ribose and deoxyribose is that deoxyribose lacks an oxygen covalently bonded to carbon 2.
• How are the components of a nucleotide connected?

  The nitrogenous base connects to pentose off of carbon 1

  The phosphate group connects to pentose off of carbon 5
• What is the sugar-phosphate backbone?

  The backbone consists of alternating pentoses and phosphates, which are linked through phosphodiester bonds. These phosphodiester bonds are formed through condensation reactions, in which water is removed.

  The ends of the backbone are identified as 5' and 3'.

  The 5' end ends with a phosphate

  The 3' end ends with a pentose

  In DNA, there are two sugar-phosphate backbones, hydrogen bonded to one another forming an anti-parallel, helical structure through complimentary base pairing.

  In RNA, however, there is one sugar-phosphate backbone, which depending on the type of RNA, (mRNA, tRNA, rRNA), can twist and bind to itself.
• What is RNA?


  RNA is a nucleic acid that consists of one chain of nucleotides.

  mRNA encodes proteins

  tRNA acts as an adaptor between mRNA and amino acids

  rRNA forms the ribosome
• Where is DNA located within a eukaryotic cell?

  Most DNA is located in the nucleus of a cell. A small amount of DNA is also located in the mitochondria and in chloroplasts.
• Where is DNA located within a prokaryotic cell?

  DNA in prokaryotes is contained in the nucleoid, not contained by a nuclear membrane. Many prokaryotes also have plasmids of small, circular DNA molecules.
• Where is RNA located within an eukaryotic cell?

  All RNA is made in the nucleus (transcription) and then transported out of the nuclear pores to the cytoplasm for translation.

  rRNA becomes part of the 80s ribosomes bound to the rER or free ribosomes.

  mRNA are exported into the cytoplasm where they are translated at ribosomes to produce proteins.

  tRNA is found in the cytoplasm where they perform their function of delivering amino acids to growing polypeptides during translation.
• Where is RNA located within a prokaryotic cell?

  rRNA is part of the 70s ribosomes free in the cytoplasm

  mRNA are translated at ribosomes in the cytoplasm to produce proteins.

  tRNA is found in the cytoplasm where they perform their function of delivering amino acids to growing polypeptides during translation.

  Both RNA and DNA use cytosine, adenine and guanine as bases, however, RNA uses uracil while DNA uses thymine. Therefore, in complimentary base pairing in RNA, A pairs with U rather than T like in DNA.