1.5 Flashcards
What is the monomers of DNA and RNA
Nucleotides
What does each nucleotide consist of
Phosphate group, nitrogenous base and a pentose sugar
What are the 2 possible pentose sugars in a nucleotide
Ribose or deoxyribose
What is a pyrimidine
Single ring structure
Cytosine and thymine and uracil
What is a purine
Double ring structure
Guanine and adenine
What are the 4 nitrogenous bases
Guanine Cytosine Adenine Thymine - DNA Uracil - RNA
What is ATP
Adenosine Triphosphate
Nucleotide
Ribose sugar, adenine base and 3 phosphate groups
How does ATP supply energy
ATP--> P + ADP + 30.6kjmol • high energy bond between 2 and 3 phosphate group • broken via hydrolysis by enzyme ATPase • 30.6kJ of energy released • endergonic • adenosine diohosphate is formed • reversible
Equation for ATP hydrolysis
ATP–> ADP + Pi + 30.6kJ energy
Advantages of ATP
- quick energy release - 1 reaction 1 enzyme
- released in small amounts when needed - safe
- universal energy currency - common source of energy in all living things
Roles of ATP in cells
- anabolic reactions eg DNA synthesis
- active transport
- muscle contraction
- nerve impulse transmission
How is DNA formed
By a condensation reaction between two nucleotides 5’-3’ direction
Structure of DNA
- two polynucleotide strands - double helix
- strands run in the opposite direction - anti-parallel
- strands are held by H bonds between complementary bases
How many H bonds between guanine and cytosine
3
How many H bonds between adenine and thymine
2
What is mRNA
Messenger RNA
• singe-stranded molecule - 300-2000 nucleotides long
• produced in the nucleus during transcription
What is rRNA
Ribosomal RNA
• forms ribosomes with the addition of protein
What is tRNA
Transfer RNA
• small molecule that winds itself into a cloverleaf shape
• has an anticodon at one end
• amino acid at the other
• transfers correct AA to growing polypeptide during translation
What are the 2 functions of DNA
Protein synthesis
Replication
Conservative replication
Semi-conservative replication
Dispersive replication
Theory of conservative replication
Original parent double-strand molecule is conserved, and a new double-stranded DNA molecule synthesised from it
Theory of semi-conservative replication
parental strands separate, and each strand acts as a template to synthesis a new strand. The new molecule consists of one original parent strand and one newly synthesised strand.
Theory of dispersive replication
the newly synthesised molecules contain fragments from the original parent strand and newly synthesised DNA
Process of semi-conservative DNA replication
- DNA helixase breaks the hydrogen bonds between bases causijg the double helix to unwind and separate into 2 strands
- Free nucleotides in the nucleoplasm bind to exposed base on DNA template strand
- DNA polymerase binds to the complementary nucleotides forming the phosphodiester bond
- One strand acts as the template for the new molecule, so newly synthesised DNA contains one parents strand and a complementary newly synthesised strand
What was the name of the experiment that determined the exact mechanism for DNA replication
Meselson-Stahl experiment
What did the Meselson-Stahl experiment involve doing?
- Growing bacteria on a 15N medium so the DNA would be a heavier weight so when extracted by centrifuging the CsCl there would be a low band
- Growing bacteria on a 14N medium for 1 generation to form a intermediate band - DNA has 1 heavy parent strand and 1 newly synthesised light strand
- Growing bacteria again in 14N for another generation to form 1 intermediate band and 1 lighter band
Which step in Meselson-Stahl experiment ruled out conservative replication
2
Would have 1 heavy and 1 light
Which step in Meselson-Stahl experiment rules out dispersive replication
3
Half of DNA intermediate and half light
What is a codon
The triplet of bases in mRNA that codes for a particular amino acid, or a punctuation signal
What are the three steps of protein synthesis
Transcription - in nucleus
Translation - at ribosomes
Post-translational modification - in Golgi
What happens during transcription
Definition
DNA acts as a template for the production of mRNA
What is an intron
non-coding nucleotide sequence in
DNA and pre-mRNA, that is
removed from pre-mRNA, to
produce mature mRNA.
What is an exon
nucleotide sequence on one strand of the DNA molecule and the corresponding mRNA that codes for the production of a specific polypeptide.
Do prokaryotes contain introns
No - mRNA directly produced from DNA template
Describe structure of tRNA
- at one end there are 3 exposed bases - anticodon
* opposite end - amino acid attachment site
What is amino acid activation
Attachment of the relevant amino acid to the attachment site
Requires ATP
Which subunit of the ribosome binds to mRNA and which to tRNA
Smaller - mRNA
Larger - tRNA binds to one of 2 attachment sites on it
What does translation involve
Converting the codons on the mRNA into a sequence of amino acids
Describe the process of translation
- INITIATION - ribosome attaches to the start codon
tRNA molecule with complementary anticodon to the first codon binds to the first attachment site on the ribosome - ELONGATION - Second tRNA molecule joins to the second attachment site
Ribosomal enzyme catalyses the formation of a peptide bond between the 2 amino acids
The first tRNA molecule is released and the ribosome now moves one codon along the mRNA which exposes a free attachment site and another tRNA molecule joins and the process is repeated - TERMINATION - a stop codon is reached and the polypeptide is released
What is a polysome
Several ribosomes bind to a single mRNA strand at the same time
Why can ATP be called the ‘universal energy currency’
Common energy source used in all living organisms
Describe the process of transcription
•DNA helicase acts on a specific region of the DNA molecule called the
cistron, breaking the hydrogen bonds between both DNA strands, causing
the strands to separate and unwind, exposing nucleotide bases.
• Free RNA nucleotides pair to exposed bases on the DNA template strand and RNA polymerase joins them by forming the phosphodiester bonds between the phosphate group on one nucleotide and the ribose sugar on the next.
• This continues until the RNA polymerase reaches a STOP codon, when the RNA polymerase detaches and production of mRNA is complete.
• The mRNA strand leaves the nucleus via the nuclear pores and moves to the
ribosomes.
