2.1.3 Nucleotides And Nucleic Acids Flashcards
What are nucleotides made of
Made of a deoxyribose pentose sugar, a nitrogenous base and a phosphate group
Describe the structure of DNA
Is a molecule with a double helix structure which consists of hydrogen bonds between complementary base pairs
What is a phosphodiester bond
Is a covalent bond between two nucleotides resulting in a condensation reaction
What are the complementary bases
Adenine - Thymine
Cytosine - Guanine
(Adenine - Uracil in RNA)
What are are the two types of bases and what are they
Pyrimidines - single ring structure - Thymine , Cytosine , Uracil
Purine - double ring structure - Adenine , Guanine
How does the structure of DNA relate to its function
- it has base sequences to store genetic information
- it is large to store massive amounts of genetic information
- it is a helix shape so that it is compact
- it has a sugar phosphate backbone for stability and protection and to reduce mutations
- it has hydrogen bonds between bases to break and reform to allow replication and for protein sythesis
What is the steps for DNA extraction in the method DNA purification
- grind the sample to break down the cell walls
- mix sample with a detergent as it disrupts the phospholipid bilayer of the cell membranes and nuclear membranes, releasing the DNA
- add salt as it breaks down the hydrogen bonds between the DNA and water molecules
- heat in water bath as the detergent and the heat also disrupts and heat also denatures the enzymes released from the cell that would otherwise begin to digest DNA
- filter to remove cell debris and membrane fragments- filtrate now has DNA and its associated proteins
- add protease to denature and break down proteins
- add ethanol to cause DNA to precipitate as nucleic acids are insoluble in ice-cold ethanol
- extract DNA
How many hydrogen bonds in the base pairs
A-T - 2 hydrogen bonds
G-C - 3 hydrogen bonds
What are the differences between DNA and RNA
DNA - RNA
- Deoxyribose (H) - Ribose (OH)
- Hydrogen 2’ - Hydroxyl 2’
- ATCG - AUCG
- double strand - single strand
- storage molecule - transport molecule
Why are polynucleotides anti-parallel
So they can join together with complementary bases with hydrogen bonds and be held the same distance apart
What is DNA replication also known as
Semi-conservative replication
Because two identical DNA molecules are made, each with one strand from the original molecule (the conserved strand) which acted as a template strand and one new strand
What is DNA replication
Occurs in preparation for mitosis, when a parent cell divides to produce two genetically identical daughter cells- as each daughter cell contains the same number of chromosomes as the parent cells, the number of DNA molecules in the parent cell must be doubled before mitosis takes place
Describe the process of DNA replication
- Double helix untwists
- DNA is unzipped when helicase enzymes break the H bonds between bases to pairs
- Both strands act as a template for free DNA nucleotides to align and synthesis new strand and the complementary bases pair [C-G and A-T]
- Hydrogen bonds between the bases reform
- DNA polymerase joins the sugar-phosphate backbones together on the new strands with covalent bonds
- The molecules twist back into a double helix - there are now 2 identical DNA
What is continuous and discontinuous replication
Continuous - DNA polymerase binds to the end of a strand, free nucleotides added without any breaks (3’ to 5’)
Discontinuous- DNA polymerase cannot bind to the end of a strand, free nucleotides added in section, Okazaki fragments with DNA ligase (5’ to 3’)
During which phase of the cell cycle does DNA replication occur?
- S phase of Interphase
- where chromosomes double to become identical sister chromatids
Why is DNA semi-conservative
The new DNA compromises one
Why is DNA semi-conservative
New DNA molecule comprises of one original strand and one new strands
Each strands of DNA molecules as a template strand for a new double helix
What is transcription?
The first stage of protein synthesis.
Where one gene on the DNA is copied into mRNA
Because DNA is too big to move out the nuclear pore
What is protein synthesis?
- transcription then translation
- the making of proteins which have been coded for
Stage 1 of transcription?
The DNA double helix unzips using DNA helicase
Hydrogen bonds between complementary bases on the strands of DNA are broken
Stage 2 of transcription
Free mRNA ribo-nucleotides pair with complementary bases on template strand (U not T)
RNA POLYMERASE joins the ribo-nucleotides together to form an new RNA polymer chain
What is the third stage of transcription?
The mRNA is completely copied and is modified then leaves the nucleus to the ribosome
What are introns and extrons
Introns are sequences of bases in the DNA which do not code for amino acids - need to be spliced out
Exons are coding regions of the DNA
What are triplets
Three nucleotide bases on DNA which form triplet codons
