2.1.3 Nueclotides and Nucleic Acids Flashcards
What are the two types of nucleic acid?
- DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
What does the base sequence of DNA code for?
The sequence of amino acids in a polypeptide
What monomers are nucleic acids, and what components are these monomers made from?
Nucleotides
- phosphate
- pentose sugar
- organic nitrogenous base
How do the pentose sugars used differ between DNA and RNA?
- DNA has pentose sugar deoxyribose (Missing an oxygen)
- RNA has pentose sugar ribose
Explain why bases are referred to as ‘organic’ and ‘nitrogenous’ and name the 5 different bases
Organic - contain carbon
Nitrogenous - contain nitrogen
Types of base
- adenine
- thymine
- cytosine
- guamine
- uracil
How do DNA and RNA differ in the bases they contain?
DNA: A,T,G,C
RNA: A,U,G,C
What do nucleotides link together to form, and how are these created?
Polynucleotides
- formed by condensation reactions
- phosphate group at the 5thcarbon of pentose sugar (5’) forms covalent bond with OH group at 3rd carbon of pentose sugar (3’) of adjacent nucleotide
- phosphodiester bond formed between nucleotides
- sugar + phosphate form strong phosphate-sugar backbone
Give key aspects of DNA
- double stranded
- polynucleotide strands run antiparralel - joined by hydrogen bonds
- base pairing - A+T (2 H bonds), G+C (3 H bonds)
Who proposed this structure of DNA?
Watson and Crick
What is the difference between purines and pyrimidines, and which bases are which?
Purines - larger, 2 sections
- adenine
- guanined
Pyrimidines - smaller, 1 section
- thymine
- cytosine
What is chargaff’s rule?
- A must pair with T
- G must pair with C
- equal amounts of adenine and thymine
- equal amounts of guanine and cytosine
Compare DNA and RNA
Pentose sugar: DNA = deoxyribose, RNA = ribose
Pyrimidine base: DNA = C or T, RNA = C or U
Purine base: DNA = A or G, RNA = A or G
No. polynucleotide strands: DNA = 2, RNA = 1
No. nucleotides: DNA = 100,000s, RNA = 100s
Types of molecule: DNA = 1, RNA = 3 - rRNA, tRNA,mRNA
What is DNA replication and where does it occur?
DNA is replicated in the nucleus
Explain the steps of semi-conservative DNA replication
- DNA unwinds ( gyrase enzyme)
- Strands speperate (helicase enzyme breaks H bonds)
- Free DNA nucleotides pair with complmentory bases
- H bonds form between pairs
- sugar phosphate backbone formed (DNA polymerase enzyme)
- Two identical copies of DNA formed
What happens if replication errors occur?
- daughter cells dont revieve genetic information
- proteins don’t function or aren’t made
- new cells don’t function or aren’t made
What is meant by semi-conservsative replication?
Each DNA molecule consists of one old strand and one new strand
Name 3 main models put forward for DNA replication
- conservative
- semi-conservative
- dispersive
Explain how Meselson and Stahl proved the semi-conservative model
- grew E. coli bacteria in a medium with heavy nitrogen (15N)
- transferred the bacteria to a medium with light nitrogen (14N)
- took DNA samples at intervals after the transfer
- Separated the DNA samples using centrifugation
- after one generation: found DNA containing both heavy and light nitrogen
- after two generations: observed both hybrid and light DNA.
What is DNA synthesis and where does it occur?
Making proteins in the nucleus and ribosomes
Why is transcription and mRNA needed?
- DNA is too large to leave the nucleus
- DNA is transcribed into mRNA which leaves through nuclear pores
- mRNA attaches to ribsome for translation
Explain the steps of transcription
- DNA unwinds in region coding for a gene
- Hydrogen bonds broken between DNA bases, so strands seperate (RNA polymerase)
- Bases of free RNA nucleotides bond with bases of DNA nucleotides - makes template strand on DNA
- Phosphodiester bonds form betwwen nucleotide bases (RNA polymerase enzyme)
- mRNA copy seperates from template and leaves nucleus via nuclear pores
Explain the key aspects of ribosomal RNA
- composed of two subunits - one large and one small
- subunits composed of proteins + rRNA
- ribosome holds mRNA in place while it is translated
Explain the key aspects of transfer RNA
- made from a strand of RNA so that end of molecule has 3 bases (anticodon)
- anticodon binds to complementary codon on mRNA
What are the stages of protein synthesis?
- Initiation
- Elongation
- Termination
