DNA & RNA (DOESN'T INCLUDE PROTEIN SYNTHESIS) Flashcards
DNA
~ Stands for deoxyribonucleic acid
~ Linked by pairs of chemicals called bases
What shape is DNA?
Double helix
Who discovered DNA is in the form of a double helix?
Watson and Crick
Structure of a nucleotide
Contains a phosphate, deoxyribose and a base
DNA structure
DNA is made up of nucleotides which are arranged in long chains called polynucleotides
Bases
There are four nitrogenous bases two are classified as purines and two are classified as pyrimidines
Purine bases
Adenine and guanine
Pyrimidine bases
Thymine and cytosine
What bases link together?
~ Adenine links with thymine ; two weak hydrogen bonds
~ Guanine links with cytosine ; three hydrogen bonds
Double helix
~ Outer two strands of the double helix are composed of deoxyribose and phosphate
~ The base pairs are between these
The Genetic Code (code for producing a protein)
~ Genes are made up of DNA which are required for the production of a protein
~ DNA codes for each amino acid by a sequence of three consecutive bases known as a triplet or codon
~ Each triplet forms a specific amino acid
~ A long chain of triplets form a protein1
Non-coding / junk DNA
Has no known function
RNA (Ribonucleic acid)
~ Needed for protein synthesis
~ One base is different, uracil replaces thymine
DNA vs RNA
DNA = longer strand, sugar is deoxyribose, has base thymine, self replicating, found in the nucleus, mitochondria and chloroplast
RNA = shorter strand, sugar is ribose, has base uracil, not self replicating, found in the nucleus, ribosome and cytoplasm
Mechanism of DNA replication
- The double helix unwinds
- An enzyme breaks the bonds between the base pairs
- DNA bases that are normally present in the cytoplasm enter the nucleus and attach themselves to exposed complimentary bases
- Each new strand is half new DNA and half original DNA. It is identical to the original DNA strand and to the other new partner strand
- Each new piece of DNA rewinds to form a double helix
What is the significance of DNA replication?
DNA is able to produce exact copies of itself, this means that the same DNA is passed on to each new generation of cells
DNA profiling
Generating a pattern of bands from a DNA sample, which can then be used to distinguish that DNA from another
Method of preparation
- DNA is released
- DNA is cut into fragments
- The fragments are separated
- Patterns are compared
- DNA is released
DNA is released and isolated
- DNA is cut into fragments
The isolated DNA is cut into fragments using restriction enzymes
- The fragments are separated
~ The fragments are separated on the basis of their size by gel electrophoresis
~ The fragments are placed in a tank containing a sugar-based gel, with an electrical current being passed through it
~ The current draws the negatively charged DNA to one end of the end
- Patterns are compared
Pattern is analysed and compared
Applications of DNA profiling
~ Crime (Forensic cases)
~ Medical
Genetic screening
Testing of DNA for the presence or absence of a gene
Methods of genetic screening
- Adult screening = Some adults might not suffer from a genetic disorder but might be a carrier of a defective gene and could possibly pass this defective gene onto their child
- Foetal screening = Cells are removed from the placenta or the fluid around the foetus and tested for a number of genetic disorders
Ethics of genetic screening
~ Adults: if the results of genetic tests became public, the people concerned may
suffer embarrassment or be treated unfairly.
~ Foetal: it could encourage a termination if a severe defect was found.
