Nucleic acids Flashcards
Draw the structure of a nucleotide
Use google or textbook
What are purine bases?
- 2 rings to their structure
- Adenine, guanine
What are pyrimidine bases?
- Single ring
- Cytosine, thymine
Describe the formation of the nucleotide
- The pentose sugar attaches itself to the phosphoric acid at carbon 5
- The pentose sugar attaches itself to the organic base at carbon 1
- The nucleotides are strung together to form a nucleic acid where the backbone is made up of alternating sugar and phosphate groups.
What is the bond between the pentose sugar and phosphoric acid called?
Ester bond
What is the bond called between two nucleotides?
Phosphodiester
What is the purpose of phosphodiester bonds?
It forms the sugar phosphate backbone of DNA
Describe the structure of DNA
- Double helix
- Two polynucleotide chains joined together by organic bases which have a complementary structure to each other.
- The bond that holds bases together= H bonds
- Nucleotides are produced by phosphodiester bonds which is a type of condensation reaction
- Complementary base pairing
- Strands run antiparallel
Describe the structure of RNA
- Contains ribose (contains oxygen)
- Single strand
- Contains uracil instead of thymine
- Shorter chain than DNA
Name some adaptations of the DNA molecule to its function.
- It is a stable molecule held together by covalent bonds= not easily broken down, forms the SPBB
- Able to copy itself accurately= due to complementary base pairing
- The DNA molecule can fold itself up = Great deal of information can be stored in a small volume
- Carries information coded in the order of the bases which can be easily copied
- H bonds are easily broken = Allows replication and protein synthesis
- H bonds are protected by being on the inside of the molecule = the two SPBB’s give protection to the base sequence from any interference
Name some adaptations of RNA to its function.
- It is single stranded= mRNA can carry a copy of DNA code with the bases exposed
- It is smaller= can travel out of the nucleus and move around the cell
- It forms base pairs with the correct tRNA molecule to control the sequence of amino acids in a pp chain
Describe semi-conservative replication! (7)
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- The DNA double helix is untwisted a bit at a time, catalysed by gyrase enzymes
- Hydrogen bonds between the nucleotide bases are broken, catalysed by DNA helicase which results in two single strands of DNA with exposed nucleotide bases, kept apart by binding proteins.
- Free phosphorylated nucleotides are bonded to the exposed bases following complementary base pairing rules. H bonds form, bringing the 2 strand together.
- The enzyme DNA polymerase joins nucleotides continuously in the 5’-3’ direction, creating the leading strand.
- In the 3-5 direction, polymerase joins nucleotides in short sections which are later joined by DNA ligase. This is called the lagging strand.
- The leading strand is synthesised continuously whereas the lagging strand is in fragments (okazarcky fragments)
- A new strand of DNA has then been formed against each of the old strands so that two identical DNA molecules have been produced.
Explain the steps of transcription
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- A gene unwinds and unzips, H bonds break between complementary bases
- Only one DNA strand contains the code for protein to be synthesised, this is called the sense strand and it runs in the 5-3 direction, complementary RNA carries the same base sequence as the sense strand
- The other strand in the 3-5 direction as the antisense strand, it acts as a template.
- RNA polymerase catalysed the formation of temporary H bonds between RNA nucleotides and the unpaired DNA bases which are complementary.
- RNA nucleotides are then joined together by H bonds using the coding strand. This creates mRNA
- The mRNA peels off of the coding strand and passes out of the nucleus through the pores in the NE and attaches to a ribosome.
Explain the steps of translation
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- Ribosome is made of two subunits; RNA and rRNA
- mRNA binds to a specific site on the smaller subunit and is held in place until it has completely translated the sequence of amino acids.
- tRNA carries the amino acids to the ribosome
- tRNA is folded so the anticodon is at one end. The anticodon is the triplet code that will recognise a specific codon in an mRNA molecule.
- Once the anticodon binds to a complementary codon on the mRNA, the corresponding amino acid joins with the previous amino acid. This forms peptide bonds and creates the primary structure of the protein.
What are the 3 features of the genetic code?
- It is near universal, almost all organisms have the same triplet of DNA bases to code for the same amino acids
- Degenerate, there is more than one base triplet that codes for the same amino acid, this reduces chance of damaging mutations
- No overlapping, read from a fixed point in groups of 3 bases (discreet 3’s)
How can mutations be caused?
- Spontaneous errors in DNA replication or meiotic recombination
- Radiation, viruses, mutagenic chemicals
- Hypermutation
What is dispersive replication?
Part but not all of each strand of the old DNA molecule becomes part of the new ones with bits scattered in amongst the old
What is Conservative replication?
A completely new DNA molecule is made with two new strands and the original one stays intact
What is Semi-conservative replication?
One new strand of DNA forms against each of the original strands so that each new DNA molecule is made up of one new and one original strand.
What does washing up liquid do
Breaks down lipids in phospholipid bilayer of plasma membrane and nuclear envelope so DNA can ‘escape’
Why is the solution containing crushed strawberry, salt and washing up liquid placed in a 60C bath?
It speeds up the reaction of washing up liquid and salt
What does the salt in the solution do?
Salt is charged as well as DNA, salt breaks the bond between histones so DNA is unravelled.
What does ethanol do?
DNA is not soluble in ethanol so it will not dissolve, it is used to separate DNA from the mixture.
What does protease do?
- Breaks down histone proteins into amino acids so DNA is released
- Purifies DNA
