Nucleic Acids and Their Functions Flashcards
What is a polynucleotide?
A molecule containing nucleotides, can comtain thousands
What are the two groups of organic bases?
Purine- double ring structure.
Pyramidine- single ring structure
What are the 2 purine cases?
Adenine
Guanine
What are the 3 pyramidine bases?
Cytosine
Thymine
Uracil
What replaces thymine in RNA?
Uracil
How is DNA structured?
Two polynucleotide strands wound into a double helix
Pentose sugar = deoxyribose
Sugar + phosphate groups on outside, form sugar-phosphate backbone.
Bases of the 2 strand face inwards and form complimentary base pairs.
How is the double helix maintained?
Hydrogen bonds form between the complementary base pairs
A-T = 2
C-G = 3
What are the carbon atom units at each end of a strand?
C3 at one
C5 at the other
The two strands are antiparallel, what does this mean?
The nucleotides are arranged in the opposite direction to those in the other strand
What are the 4 ways in which DNA’s structure helps its function?
- very stable so genetic info passes unchanged to each gen
- very large molecule so can carry large genetic info amount
- 2 strands can separate as only held by hydrogen bonds
- genetic info protected by sugar-phosphate backbone
What is RNA’s structure?
1 polynucleotide stran
Pentose sugar is ribose
What does mRNA do and where is it made?
Carries genetic code from DNA to ribosomes
Synthesised in nucleus
What is the function rRNA and where is it found?
Combines with protein to make ribosomes
Found in cytoplasm
How is tRNA (transfer) structured?
Each molecule has 3 base sequence called anticodon- Complementary to codons on mRNA.
Has amino acid attachment site. Each molecule is specific to an amino acid.
What are the 2 major functions of DNA?
Replication for cell division
Carryjng genetic code for protein synthesis in all cells.
How does replication occur?
Chromosomes make copies of themselves so that when cells divide, each daughter cell receives exact copy of genetic info.
When/where does replication take place?
Cell’s nucleus during interphase (s phase) of cell cycle.
What is transcription?
The mechanism by which the base sequence of a gene on a DNA strand is converted into the complimentary base sequence of mRNA.
Hoe does transcription occur?
DNA helicase breaks bases’ hydrogen bonds, separating 2 strands and exposing bases.
RNA polymerase binds to template strand. Free RNA nucleotides align oposite complementary bases. Polymerase moves along DNA, forming bonds that add nucleotides to RNA strand 1 at a tine.
mRNA molecule synthesised. Helix rewound behind polymerase.
Polymerase separates when it reaches a stop codon.
What is a nucleotide and what is it made up of?
A monomer of nucleoc acid comprising of a pentose sugar, a nitrogenous base and a phosphate group attached to the fifth carbon of the sugar
What is translation?
The process of translating the codons in mRNA into a specific sequence of amino acids, forming a polypeptide chain at the ribosome.
What are the 3 stages of translation?
Initiation
Elongation
Termination
How does initiation occur?
Ribosome attaches to start codon at 1 end of mRNA molecule.
First tRNA, with an anticodon complimentary to first codon on mRNA,
attaches to ribosome.
The 3 bases of mRNA’s codon and tRNA’s anticodon bond with hydrogen bonds.
A 2nd tRNA with anticodon comp to 2nd codon on mRNA attaches to other attachment site and codon-ac bind
How does elongation occur?
Ribosomal enzhme catalyses peptide bond formation between the 2 amino acids. First tRNA leaves ribosome, leaving attachment site vacant.
Ribosome moves along 1 codon on the mRNA strand.
The next tRNA binds.
How does termination occur?
The sequence repeats until a stop codon is reached.
Ribosome-mRNA-polypeptide complex separates
What is added to a protein to form a glycoprotein?
Carbohydrate
What does ATP do and what is it known as?
Transports chemical energy from where it is made to where it is needed.
Universal energy currency- involved in energy changes in all living organisms
What is ATP made up of?
Nitrogenous base-adenine
Ribose sugar
3 phosphate groups
What happens when energy is needed?
Enzyme ATPase hydrolyses bond between 3rd and 2nd phosphate group, forming ADP and and inorganic phosphate ion (Pi). Chemical energy is released.
What is an exergonic reaction?
Reaction in which emergy is released
How many kJ of enegy are released per ATP mole hydrolysed?
30.6kj
How is ATP hydrolysis reversible?
ADP and Pi can combine in condensation reaction, forming ATP and water.
What is the addition of phosphate to ADP called and what is it catalysed by?
Phosphorylation.
Catalysed by ATP Synthase.
What is an endergonic reaction?
Reaction using energy
What are the 4 advs of ATP to provide energy instead of direct glucose use?
- single reaction that releases energy immediately
- only 1 enzyme needed
- releases in small amounts, when and where needed
- provides common energy sources for many reactions, increasing cell’s efficiency and control
What is gene (which DNA is divided into thousands of)?
A sequence of DNA bases that codes for one polypeptide.
How many bases encode an amino acid and what is it named?
3- triplet code.
How many possible codes are there?
64
What codon always starts the amino acid chain?
Methionine (AUG)
What are the 3 stop codon codes?
UAA, UAG, UGA
What is pre-mRNA?
The mRNA directly after being formed , needs to be processed before synthesing proteins.
How is pre-mRNA processed?
Introns are removed by endonuclease enzymes. The remaining base sequences, the exons are joined together by ligase enzymes.
What are inteons?
Sequences of bases in pre-mRNA that aren’t needed for protein production.
What are the 3 DNA replication theories?
Conservative replication theory
Semi-conservative replication theory
Dispersive replication theory
What is the conservative replication theory?
Parental DNA double helix remains intact and. Whole new double helix is made from 2 strands of entirely new material.
What is the semi-conservative replication theory?
Parental double helix separates into 2 strands, each acting as a template for sythesis of a new strand.
Each new DNA molecule will contain 1 new strand and 1 parental strand.
What is the dispersive replication theory?
2 copies of the DNA double helix are formed.
Each new molecule will contain distinct regions of DNA composed from the parental strands.
Part of Meselson and Stahl’s experiments need to know:-
DNA from first gen culture was extracted and centrifuged, settling at a mid point in the tube.
=ruled out conservative the entirely heavy 15n parental band would’ve been produced.
Proven DNA replication method:-
Semi-conservative
Proven DNA replication method:-
Semi-conservative
