DNA Flashcards
What are nucleic acids, what are two different types, and what do they do?
Nucleic acids are polymers made out of nucleotides
DNA = holds genetic information
RNA = transfers genetic information from DNA to the ribosomes
What is the structure of DNA?
- a double helix with two polynucleotide chains held together by hydrogen bonds between complementary base pairs
- pentose sugar (because it has 5 carbons ) =deoxyribose
- phosphate group
- a nitrogen-containing organic base : cytosine, thymine, adenine, guanine
What chemical reaction forms a nucleotide and what bond is created when two nucleotides undergo this chemical reaction?
condensation reaction
A condensation reaction between two nucleotides forms a phosphodiester bond
What is the difference between DNA and proteins?
DNA is a sequence of bases but proteins are a sequence of amino acids
What is the structure of RNA?
- relatively short polynucleotide chain
- pentose sugar = ribose
- phosphate group
- a nitrogen-containing organic base: cytosine, uracil, adenine, guanine
What is the function of RNA?
transfers genetic information from DNA to ribosomes rather than holds information (like DNA)
Draw the structure of a phosphodiester bond
What is the base paring for DNA?
adenine = thymine
guanine = cytosine
Why is DNA a stable molecule?
- the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights
- because there are three hydrogen bonds between cysteine and guanine, the higher proportion of C—G pairings, the more stable the DNA molecule
How is DNA adapted to carry out its function?
- very stable structure. Rarely mutates
- two separate strands are joined only with hydrogen bonds, which allows them to separate during DNA replication and protein synthesis
- extremely large molecule and therefore carries an immense amount of genetic information
- by having base pairs within the helical cylinder of the deoxyribose-phosphate backbone, the genetic information is to some extent protected from being corrupted by outside chemical and physical forces
- Base pairing leads of DNA being able to replicate and to transfer information and mRNA
Name the two purine bases. How are they different from the pyrimidine bases? (name all the pyrimidine bases)
- The bases adenine and guanine are purines
– they have a double ring structure - The bases cytosine, thymine and uracil are pyrimidines
– they have a single ring structure
Which bases form two hydrogen bond?
adenine and thymine
What are the two requirements for semi-conservative replication?
- the four types of nucleotides (each with a different base) must be present
- a source of chemical energy to drive the process
What does semi-conservative replication of DNA ensure?
genetic continuity between generations of cells
Describe the anti-parallel nature of DNA
As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’ strand and the other is known as the 3’ to 5’ strand
Draw a dna polynucleotide
How many bases make up an amino acid?
3
Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA? (2 marks, 3 possible answers)
1- Weak hydrogen bonds between bases allow two strands to unzip
2- 2 strands exists, both of them can act as template for replication
3- Complementary base pairing, this allows accurate replication
why may a gene contain more than the necessary amount of bases it needs
because there are regions of the gene that are non-coding
Describe the process of translation?
A molecule of mRNA leaves the nucleus via a nuclear pore and binds to a ribosome.
6 bases are attached to the small subunit of the ribosome these are read as two codons.
tRNA with complementary anticodons, form weak hydrogen bonds with the complementary codons, bringing with it a specific amino acid.
A second tRNA molecule bearing a different amino acid binds to the second codon with its complementary anticodon.
Using an enzyme to catalyst the reaction and ATP for energy, peptidebonds form between the two adjacent amino acids.
The ribosomes now moves along the mRNA, reading the next codon. A third RNA molecule brings another amino acid and a peptide bond forms.
The first tRNA leave and is able to collect another one of its amino acids. The polypeptide chain grows until a stop codon is reached
Describe the process of transcription? (exam-based)
occurs in the nucleolus of the nucleus
DNA Helicase breaks the hydrogen bonds between complementary bases in the gene
the double strand of the gene unwinds and the nucleotide bases are exposed
One of the separate DNA strands acts as a template.
Free RNA nucleotides align to exposed bases on the template strand by complementary base pairing, with Uracil pairing with adenine and guanine pairing with cytosine.
RNA Polymerase moves along the strands, joining the nucleotides together with phosphodiester bonds to form the sugar-phosphate backbone of the RNA strand.
RNA polymerase reaches a stop codon and then detaches, resulting in the formation of pre-MRNA
pre- MRNA is then spliced, to remove introns and leaves only exons to produce mRNA
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