1.5 - Nucleic Acid Flashcards
- What is the name of the monomer that forms nucleic acids.
- DRAW the general structure and label it.
- Name the reaction and the bond formed between to monomers
- Monomer = Nucleotide
- check notes
- Condensation reaction forms phosphodiester bonds between the phosphate group of one nucleotide and the sugar of another nucleotide
- What does DNA stand for?
- DRAW the general structure of DNA and label it
- Deoxyribonucleic acid
- Check notes
- Explain how the structure of DNA is related to its functions (mark schemes can vary, so write everything!)
Sugar-phosphate backbone
Double helix/ Coiling around histone proteins
Long molecule
Sequence of bases
Double helix with MANY hydrogen bonds between complementary base pairs
Double stranded
Double helix
Hydrogen bonds between the complementary base pairs are WEAK and can be easily broken
Complementary base pairings
Gives strength
Gives it a compact shape
Stores lots of genetic information
Allows information to be stored/ codes for amino acids
Makes the DNA molecule stable
BOTH strands can act as templates during semi-conservative replication of DNA
Prevents the genetic code being corrupted
Allows the DNA strands to be separated for DNA replication and also for transcription in protein synthesis
Allows accurate replication of DNA
What is meant by complementary base pairing?
● Each base is complementary to one other base – this is the one that it binds to
● Guanine and cytosine are complementary to each other and therefore ONLY bind to each other (3 hydrogen bonds)
● Adenine and thymine are complementary to each other and therefore ONLY bind to each other (2 hydrogen bonds)
What do we mean by ‘the strands are anti-parallel’?
The DNA strands go in opposite directions. One DNA strand goes in the 5’ to 3’ direction the other DNA strand goes in the 3’ to 5’ direction
Describe the differences between DNA and RNA (5 marks)
● DNA has thymine (A,T,C,G bases) whereas RNA has uracil (A,U,C,G)
● DNA has a deoxyribose sugar whereas RNA has a ribose sugar
● DNA is double stranded whereas RNA is single stranded
● DNA is a large polymer RNA is a short polymer
● DNA holds genetic information in the nucleus whereas RNA transports genetic information to the ribosome
Describe the differences between DNA in prokaryotes and Eukaryotes
● DNA in eukaryotes is coiled up around proteins called HISTONES whereas the DNA in prokaryotes is not
● DNA in eukaryotes is linear whereas DNA in prokaryotes is circular
● DNA in eukaryotes is found in a nucleus, whereas DNA in prokaryotes is free in the cytoplasm
● DNA in eukaryotes contains introns and exons whereas DNA in prokaryotes does not contain introns
Genes and Polypeptides
● A gene is a section of DNA located at a particular site on a DNA molecule, called its locus
● Genes are a specific sequence of bases which can code for the amino acid sequence of a polypeptide or functional RNA (e.g. ribosomal RNA and tRNA)
● 3 bases on DNA are called a TRIPLET CODE, 3 bases CODE for 1 amino acid. Each triplet codes for a SPECIFIC amino acid
● What is the link between DNA bases, amino acids and a protein? A sequence of bases codes for a sequence of amino acids to form a polypeptide chain, which can fold into a protein
In eukaryotes, much of the nuclear DNA does not code for polypeptides, we call it the non-coding region
The following are examples of non-coding regions. Define the terms
● Introns - non-coding sequences/ regions of DNA within a gene
● Non-coding multiple repeats – non-coding sequences/ regions of DNA found between genes
However, exons are the coding sections of a gene (i.e. the sequences of DNA that codes for amino acids)
DNA and its features – define the following terms
● Universal = each triplet codes for the same amino acids in all organisms
● Non-overlapping = each base is only used in one triplet code
● Degenerate = Some amino acids are coded for by more than 1 triplet code/codon
Define Genome
● the complete set of genes in a cell
Define Proteome
● the full range of different proteins that a cell is able to produce at a given time
Why might changing the base sequence of a gene lead to a non-functional protein being formed?
- Different base sequence
- Codes for a different sequence of amino acids (different primary structure)
- Hydrogen, ionic and disulphide bonds form between different R-groups
- Different tertiary structure
- Protein is a different shape, so it is non-functional
● Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.
o Watson and Crick
● Describe the process of DNA replication
o Helicase breaks the hydrogen bonds between complementary base pairs and the 2 polynucleotide strands separate
o Both DNA strands act as templates
o Free DNA nucleotides attach to each strand by
o complementary base pairing (Adenine binds with Thymine and Guanine binds with Cytosine)
o Hydrogen bonds form between the complementary base pairs
o DNA polymerase forms phosphodiester bonds between the adjacent DNA nucleotides on the new strand, through condensation reactions
o Two new DNA double helices are made: each DNA double helix consists of one old strand of DNA and one new strand of DNA. This is called semi-conservative replication
● Why is DNA replication described as being ‘semi-conservative’?
o Because both DNA strands/ each DNA strand act as templates, and each new DNA double helix is made of one old strand of DNA and one new strand of DNA
● Meselson and Stahl grew bacteria on a medium containing N15.. Why is this Nitrogen different to ‘normal’ nitrogen and why was it used? (What was the Nitrogen incorporated into in the bacteria?)
o It is an isotope of nitrogen, and it is more dense. This nitrogen was incorporated into the nitrogenous bases in the DNA
● They then moved the bacteria to a medium containing N14. When they took a sample of DNA from these bacteria after they had grown on the new medium for 1 generation, what did they notice about the density of the DNA compared with DNA from the original bacteria? Explain your answer.
o The DNA from the bacteria which had grown on N14 for one generation was less dense than the DNA from bacteria that had only grown on N15
● After a second generation on the N14 medium they found that they had DNA double helices of 2 different densities. Explain their finding:
o Some of the DNA double helices consisted of one strand of DNA that contained N15 and one strand of DNA that contained N14. Some of the DNA double helices consisted of both strands that contained N14. These DNA double helices (with only N14 strands) were less dense
