Nucleic Acids Flashcards
Two types of nucleic acid
DNA and RNA
DNA and RNA are?
polynucleotides made from many nucleotides linked together in a chain. They are linked by phosphodiester bonds by a condensation reaction.
Components of a nucleotide and what type of bond does it have
A phosphate group
A pentose sugar
A nitrogenous base
Has phosphodiester bonds between phosphate and sugar
Difference between DNA and RNA?
- In DNA its pentose sugar deoxyribose while in RNA its pentose sugar is ribose. Ribose has 1 more oxygen than deoxyribose.
- DNA is double stranded while RNA is single stranded.
- In RNA thymine is replaced with uracil.
What are pyrimidines?
Smaller bases which contain a single carbon ring such as thymine and cytosine.
What are purines?
Larger bases which contain double carbon rings such as adenine and guanine.
What is the structure of DNA?
DNA is made up of 2 strands of polynucleotides running in anti-parallel directions, coiled up into a double helix.
Describe the bonds in complementary base pairing
Adenine and thymine form 2 hydrogen bonds.
Cytosine and Guanine form 3 hydrogen bonds.
Pyrimidines bases always bind to purines to maintain a constant distance between back bones.
Role of DNA and RNA
Storage of genetic information, transfer of genetic information and synthesis of polypeptides
What is DNA helicase?
DNA helicase is an enzyme that breaks down hydrogen bonds between bases. This unzips the DNA into 2 separate strands.
What is DNA polymerase
Is an enzyme that joins nucleotides together to form the phosphate backbone.
What is semi conservative?
When each new DNA molecule replicated contain one strand from the old DNA and one strand that is new.
What is mutation?
Change in the base sequence. Mutations can occur randomly or spontaneously. In mutation a base could be added, deleted or changed. Deleted or added changes all codons while changing only affects 1 codon. Some mutation can be beneficial, neutral or harmful.
What is transcription?
Copying sections of DNA base sequences to produce mRNA which is transported to the ribosome.
What is translation?
Is when mRNA is decoded by tRNA into a sequence of Amino acids
Why does DNA not leave the nucleus
So DNA does not become damaged in the cytoplasm.
Transcription
- DNA unzips and unwinds by DNA helicase
- free RNA nucleotides line up along the exposed bases by complementary base pairing.
- phosphodiester bonds form between the RNA nucleotides forming mRNA.
- transcription ends at the end of the gene and completed RNA is called mRNA.
- mRNA travels to the ribosome
Translation
- Ribosome is made from 2 subunits protein and rRNA. rRNA maintains stability and catalyses the reaction between two amino acids.
- tRNA has an anticodon which will complementary bind with a codon on the mRNA. tRNA are attached to an amino acid corresponding to the codon read. When anticodons are read amino acids are brought together in sequence. This forms the primary structure.
Degenerate code
There are 64 codons but 21 amino acids. This means some amino acids can created by different codons.
How is DNA replicated
- DNA helicase breaks the hydrogen bonds between the 2 polynucleotide DNA strands. The helix unzips to form two single strands.
- Each single strand act as a template for a new strand and free floating DNA nucleotides join to the exposed bases by complementary base pairing.
- The nucleotides on the new strand are joined together by the enzyme DNA polymerase. This forms the sugar phosphate back bone and hydrogen bonds form between bases.
- The strand twists to form a double helix. Each new DNA molecule contains one strand from the original and one new one. This is semi conservative replication.
