2.1.3 Nucleic Acids Flashcards
Explain the process of DNA replication
- DNA molecule unwinds - catalysed by GYRASE enzyme
- unzips- bonds between nucleotide bases are broken. catalysed by DNA HELICASE.
- free phosphorylated nucleotides are bonded to the exposed bases via complementary base pairing
- DNA POLYMERASE joins the nucleotides by catalysing formation of phosphodiester bonds between them, in 5’ to 3’ direction.
- LEADING STRAND: synthesised continuously
LAGGING STRAND: in fragments and then these are joined. DNA LIGASE catalyses phosphodiester bond formation between these okazaki fragments
What is tRNA? Where’s it made, structure, function.
- made in nucleolus
- smaller than mRNA and DNA
-single stranded polynucleotides that twists into clover shape
-one end has trio of nucleotide unpaired bases that attaches to a specific amino acid
-opp end hasanticodon complementary to specific codon on mRNA.
What is the structure of RNA?
ribose sugar, nitrogenous base uracil instead of thymine
polynucleotide chain is usually single stranded and shorter
3 forms: mRNA, tRNA, rRNA
What is the structure of DNA?
polymer made of nucleotides
2 polynucleotide strands that are antiparallel, twisted into double helix. with phosphodiester bonds
each DNA nucleotide consists of a phosphate group, deoxyribose, and one of the four nitrogenous bases adenine, guanine, cytosine, thymine.
long: carry lots of encoded genetic informartion
What is the structure of ADP?
- pentose sugar ( ribose), nitrogenous base (adenine) and 2 inorganic phosphates
What is the structure and function of ATP?
pentose sugar (ribose), nitrogenous base (adenine) and inorganic phosphates
function:
used in most energy-requiring metabolic processes
What is the product of DNA replication?
2 DNA molecules identical. Each contains 1 old strand and 1 new strand = semi- conservative replication
What is the importance of hydrogen bonding in DNA?
between nitrogenous bases
complementary base pairing: A pairs with T via 2 H BONDS, C pairs with G via 3 H BONDS.
uniform width across molecule due to pairing of purines with pyrimidines and twists into double helix.
large no. of H bonds = stability, but can be broken for transcription and replication.
What is the importance of DNA replication?
so that each new daughter cell receives the same full set of instructions
DNA in chloroplasts and mitochondria also replicates
What is DNA?
- a nucleic acid macromolecule (very large polynucleotide)
-deoxyribonucleic acid
what is dispersive replication?
- molecules are a mix of old and new - original molecule breaks up into nucleotides
What is conservative replication?
- original molecule acts as template and a new molecule is made with new nucleotides ( 2 new strands in one molecule)
what is adenosine?
- nucleoside: sugar and base
What helps ribosomes to bind together? What are ribosomes made of?
mag ions help bind two ribosome subunits
rRNA and protein
Explain the process of transcription
- Gene unwinds and unzips. H bonds between nucleotide bases break. RNA helicase
- Formation of temporary hydrogen bonds between free RNA nucleotides and their complementary unpaired DNA bases on the template strand occurs.
- RNA polymerase catalyses the joining of RNA nucleotides by forming phosphodiester bonds
- A length of complementary RNA to the template strand is produced. Copy of DNA coding strand.
- Introns are removed from this mRNA, to leave only exons
- it pases out of nucleus via nuclear envelope and attaches to ribosome.
Explain the process of translation
RNA is attached to ribosome in cytoplasm or RER
tRNA molecules bring amino acids and find their place when its anticodon binds by temporary H bonds to the complementary codon on the mRNA
2 adjacent amino acids = peptide bond formed
a polypeptide assembled. mRNA breaks down and its component molecules can be recycled.
newly synthesised protein is helped by chaperone proteins to begin folding
What evidence is there for semi-conservative replication?
Grew E. coli in medium containing a “heavy” isotope of nitrogen (N15), used it to synthesize DNA. Gen 0 = only N15 (one single heavy band)
Then after Gen 0, the bacteria were switched to medium containing a “light” N14 isotope and allowed to grow for several generations. They then measured the density of the DNA.
Generation 1
Higher single band- intermediate in density between the heavy and light. DNA molecules was a hybrid of light and heavy DNA. Doesnt fit with the conservative model.
Generation 2
Showed DNA was being replicated semi-conservatively. The pattern of two distinct bands—one at the position of a hybrid molecule and one at the position of a light molecule. in dispersive replication, it would be impossible to get a “purely light” molecule.
Generations 3 and 4
over the third and fourth generations, we’d expect the hybrid band to become progressively fainter and the light band to become progressively stronger
What does translation require?
ATP
What does it mean by the antiparallel sugar phosphate backbone?
‘opp directions’ of 2 strands = direction that C3 or C5 are facing.
one end: C5 of pentose is nearest to end = 5’ end
other end: C3 of pentose is nearest to end= 3’ end
What does each gene contain?
sequence of DNA base triplets that determines the sequence (primary structure) of amino acids in a particular polypeptide
what do they become when they have more than one phosphate group?
PHOSPHORYLATED nucleotides
for example, ADP ( adenosine diphosphate)
What are some features of the genetic code?
- near universal: in almost all living organisms the same triplet of DNA bases code for the same amino acid
- degenerate: for all amino acids except tryptophan and methionine, there is more than one base triplet that can code for it -reduces effect of point mutations
- non overlapping + read starting from a fixed point in groups of 3 bases, with no bases being part of more than one triplet.
what are purines and pyrimidines?
purine: two rings, A or G
pyrimidines: one ring, T or C or U
What are nucleotides? (structure)
- nitrogenous base linked to C1 of sugar, and a phosphate group linked to C5 or C3 by covalent bonds
- monomers of nucleic acids
What are nucleotides used for?
help regulate many metabolic pathways e.g. ATP, ADP and AMP
may be components of many co-enzymes - adenine nucleotides = components of NADP which is used in photosynthesis and NAD involved in respiration.
How is DNA purified?
Macerating tissue to get individual cells and break cell walls etc in plants
Adding strong detergent (including salts too) to break down phospholipid bilayer and act as an emulsifier
Add protease enzyme= breaks down proteins associated with DNA
Add ethanol- DNA precipitates
How is DNA organised in cells?
eukaryotic: genome in nucleus. each DNA molecule is wound around histone proteins into chromosomes. loop of DNA without proteins in mitochondria and chloroplasts too
prokaryotic: loop in cytoplasm without proteins. also have plasmid.
- viruses that contain DNA also have it as a loop
