Chapter 3 - Nucleotides Flashcards
double ringed structures?
PURINES
Guanine, Adenie
single ringed structures?
pYrimidines
thYmine
cYtosine
Uracil
2 reasons why base pairing is so specific?
1- Purines pair with pyrimidines
2- G: C base pairs have 3H bonds
- A:T base pairs have 2H bonds
base pairing memory trick?
C is the third letter of alphabet
TA2 - Tattoo
the 2 DNA strands are _____ and form a ____ ______ molecule. this is ___ ______
anti parallel, double helix
right handed
function of DNA?
- allows cells to divide, bc it can replicate
2. contains the genetic code - instructions for protei synthesis
Extracting DNA from plant cells - chop/ grind/ liquidise
- breaks down cell walls allowing DNA to exit the cellss
Extracting DNA from plant cells -place in water bath @60 for 5 mins
- when cells are damaged, enzymes are released which easily break down DNA
Extracting DNA from plant cells - filter the blended mixture
broken down cells contain a mixture of organelles and cell fragments
Extracting DNA from plant cells - detergent
DNA is in the nucleus, behind the plasma membrane and the nuclear envelope
Extracting DNA from plant cells -addition of protease enzymes
DNA is closely associated with histone proteins
Extracting DNA from plant cells -add ice cold ethanol
DNA is soluble in water so you can’t see it in solution
what did meselson and stahl do?
- grew e-coli cells in Nitrogen 15 medium for many generations
- analyse DNA with density gradient centrifugation
- Then put sample of E-coli in Nitrogen 14 medium for 1 generation
what is semi conservative DNA replication?
- DNA molecule separates into 2 strands
- Each old strand is used as a template
- Free nucleotides are added to each strand using rules of complementary base pairing
- 2 molecules of DNA are formed, each consisting of 1 new strand and 1 old
DNA replication problem?
free nucleotides can be only be added to the 3’ and not 5’ end
what does DNA ligase do?
forms phosphodiester bonds between Okazaki fragments completing the strand
Replication bubbles?
DNA replicates from multiple origins of replication forming replication bubbles
the genetic code - universal
the fact that all life shares a universal genetic code is one of the most powerful pieces of evidence that life has evolved from a common ancestor
the genetic code - triplet code
- 20 amino acids which all proteins are made from
- triplet code - 64 AAs can be coded for - more than enough (4x4x4 = 64)
the genetic code - degeneracy
some AAs have more than one triplet coding for them. This gives the genetic code some capacity for absorbing mutations without any effect
- also gives for stop triplets - 3 of these
the genetic code - non - overlapping
- a gene always starts with the same triplet - called the start codon. this ensures that the code is always read ‘in frame’
the start codon…
sets the reading frame and ensures that triplets do not overlap
which strand is read in transcription?
DNA has 2 strands - antisense & sense. The antisense stand is read by RNA polymerase in the process of transcription to form RNA
Protein synthesis?
how a specific sequence of bases in DNA is converted to a specific sequence of AAs in a protein
2 processes in protein synthesis?
- Transcription: DNA -> mRNA
2. Translation; mRNA -> protein
tRNA?
tRNA transfers specific amino acids from the cytoplasm to the ribosome during translation
- the codon anticodon base pairing determines which specific AAs is transferred
what is a gene?
A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein
What is rRNA important for?
- maintaining structural stability of the protein synthesis sequence
- plays a biochemical role in catalysing the reaction
What is a nucleotide?
a molecule composed of a pentose sugar, phosphate group, nitrogenous base. it is the monomer unit of nucleic acids
what is a polynucleotide?
a polymer made up of many nucleotide monomers joined together by a series of condensation reactions
What did Watson & Crick discover?
DNA was composed of 2 very long polynucleotide chains twisted into a double helix
the double helix of DNA is …
anti parallel meaning the strands of DNA run in opp directions to each other
RNA is ___ stranded and shorter than ___
single, DNA
DNA rep takes place during which stage of cell cycle?
inter-phase, phase before cell begins to /
key:
- synthesis happens from 5’ to 3’
- new nucleotide added to 3’
DNA helicase ?
Is an enzyme that catalyses the breaking of H bonds between the complementary organic bases in DNA
DNA polymerase?
the enzyme that catalyses the formation of phosphodiester bonds and the adjoining od adjacent new nucleotide
Semi conservative replication definition?
the method in which DNA replicates creating 2 molecules of DNA that consist of 1 original DNA strand and one newly synthesised DNA strand
leading strand
- RNA polymerase can only add new nucleotides in 3’ to 5’ direction
- allows one strand to be synthesised continuously
lagging strand?
synthesis of other strand is discontinuous as DNA polymerase moves away from the strand
Okazaki fragments?
lagging strand is synthesised in short sections called Okazaki fragments
What is functional RNA?
The RNA that has a functional role in an organism other than coding for proteins
Transcription def?
the process of making messenger RNA from a DNA template
Translation def?
The process of making proteins by forming a specific sequence of amino acids based on coded instructions in the mRNA
what is the genetic code?
the specific sequence of bases in DNA or RNA that codes for a sequence of AAs during protei synthesis
codon definition?
a codon is a specific sequence of 3 bases of RNA and DNA that code for a specific amino acid
3 stop codons are:
TAG, TAA, TGA
- do not code for any AAs, causing translation to cease
why does tRNA have a clover leaf shape?
bc it can form complementary base paris with itself
what does the degeneracy of the genetic code mean for tRNA?
tRNAs with diff anticodons can bind to the same amino acid
what is a ribozyme?
- The RNA that exists in the large subunit is called a catalyse which catalyses the formation of peptide bonds as polypeptides are formed
- as this catalyst is an RNA molecule, not protein, it’s called a ribozyme instead of enzyme
How does translation end ?
- no tRNA molecules with complementary anti-codons for the stop codons
- so when stop codon is reached, no tRNAs can bind and the synthesised polypeptide is released from the last tRNA molecule
what is a sense strand?
the only one out of the 2 strands that contains the codons that are used to code for AAs
