Biological Molecules 2 Flashcards
What is the structure of a nucleotide?
A pentose sugar (ribose in RNA and deoxyribose in DNA)
A nitrogenous base
A phosphate group
What is the difference between a purine and a pyramidine base?
Purine has 2 nitrogen containing rings whereas pyramidine has only 1
Examples of purines and pyrimidines
Purine - adenine, guanine
Pyrimidines - cytosine, thymine, uracil
What is ATPs structure and function?
ATP (adenosine triphosphate) is a nucleotide with 3 phosphate groups attached
It is a universal energy supplier in cells and is used to fuel reactions
What is the reaction of ATP when energy is needed in the cell?
The third phosphate bond in the molecule is broken by a hydrolysis reaction
This is catalysed by the enzyme ATPase
The products of this reaction are adenosine diphosphate, another nucleotide and a free inorganic phosphate group
The energy is made when the bonds are made to produce ADP
What is the cycle of ADP and ATP
ATP = hydrolysis = ATP = condensation =ATP ….. etc.
What are nucleic acids?
The formation molecules of cells
They are polymers that carry all information needed to form new cells
How is a sugar phosphate backbone made?
Nucleic acids link together by condensation reactions to produce phosphodiester bonds between the sugar on one nucleotide and the phosphate group of the next.
Both DNA and RNA have this.
How is DNA structured?
The bases stick out for the sugar phosphate backbone and there are 2 parallel
A pyrimidine base always joins with a purine base
There are 3 hydrogen bonds between C and G but only 2 between A and T
They run opposite ways with the 5 prime strands always being parallel with the 3 prime strand
What were the 2 main ideas of how DNA replication works?
Conservative and semi conservative replication
What is the conservative model of DNA replication?
The double helix remained intact and instructed the formation of a new identical double helix made up of new material
What is semi conservative replication?
The DNA unzipped and new nucleotides line up along each strand. Each new double helix contained one strand of the original DNA and one strand of new material.
How was semi conservative replication proven?
Meselson and stahl grew E. coli with 15N nitrogen which is denser than 14N nitrogen usually found. The bacteria in this medium made up the DNA therefore having 15N DNA. They predicated if semi conservative replication was true, the outcome would have hybrid DNA and not just 15N or 14N. They found this was true.
How does DNA make copies of itself?
The 2 strands of DNA unzip along the line of hydrogen bonds and unravel which is brought about by the enzyme DNA helicase.
These strands act as template strands for the new DNA.
The exposed bases attract free DNA nucleotides and new hydrogen bonds are formed.
DNA polymerase lines up and catalyses the linking up of the nucleotides along the template strand.
DNA ligase catalyses the formation of phosphodiester bonds between the 2 strands of DNA.
Thus results in 2 new DNA strands identical to the original and the DNA strands automatically coil back up into the double helix.
What is a codon?
A sequence of 3 bases
What is the complementary strand?
The mRNA complementary strand is DNA sequence in reverse with U replacing T
What are the 3 main functions of RNA?
Carries instructions for a polypeptide from the DNA in the nucleus to the ribosomes
Picks up specific amino acids from the protoplasm and carries them to the surface of the ribosomes
Makes up the bulk of ribosomes themselves
What is the difference between RNA and DNA?
RNA is a ribose sugar and has uracil instead of thymine. It is a single helix and does not form big complex molecules like DNA.
mRNA (messenger RNA)
Formed in the nucleus
Usually has instructions for one polypeptide
mRNA forms on the antisense (template) strand of the DNA
Function of mRNA
-Parts of DNA unravel and and are transcribed onto mRNA strands by RNA polymerase
-Complementary bases of DNA and RNA line up alongside each other
-Initially hydrogen bonds hold the RNA molecules together however later RNA polymerase catalyses the formation of phosphodiester bonds between sugar and phosphate group of the bases forming a strand of RNA
-Leaves the nucleus through nuclear pores in the membrane moving to the surface of the ribosomes where protein synthesis takes place
tRNA (transfer RNA)
Found in cytoplasm and has complex shape (cloverleaf shape) as a result of hydrogen bonding
Has sequence of 3 bases corresponding to DNA called anticodon
Has a binding site to pick up a particular amino acid
tRNA function
-Molecules each carrying a specific amino acid line up alongside mRNA on the surface of the ribosome
-Anti codons of tRNA line up with codons of mRNA held in place by hydrogen bonds
-The correct sequence of amino acids is then assembled forming a chain with peptide bonds between them
rRNA (ribosomal RNA)
-Makes up 50% of the ribosome
-The most common form of RNA found in cells
-Holds together mRNA and tRNA and acts as enzymes controlling protein synthesis
Protein synthesis
-DNA is transcribed to mRNA
-mRNA moves out of nucleus into cytoplasm and attaches to a ribosome
-molecules of tRNA carry amino acids to surface of ribosome
-tRNA anticodon lines up against the complementary mRNA codon (held in place by hydrogen bonds) while enzymes link amino acids together
-tRNA then breaks away and returns to the cytoplasm to pick up another amino acid
-the ribosome moves along the mRNA until it reaches the end leaving a completed polypeptide chain
What are polysomes?
Groups of ribosomes joined by a thread of mRNA (they are a form of mass production of particular proteins)
