chapter 3 - nucleic acids and DNA Flashcards
what are the two types of nucleic acids
DNA and RNA
what are the 5 nitrogenous bases and which are specific to DNA and RNA
adenine, cytosine, guanine
thymine - only DNA
uracil - only RNA
how does the structure of DNA and RNA differ
DNA is a double helix whereas RNA is a single strand
DNA has the sugar deoxyribose and RNA has the sugar ribose
in DNA, the base adenine pairs with thymine.
in RNA, the base adenine pairs with uracil
what bonds form between nucleotides?
what do they form?
how are they formed?
phosphodiester bonds
form polynucleotides, with a sugar-phosphate backbone
the OH group from the phosphate on nucleotide 1 and
the OH from the saccharide on nucleotide 2 are removed
one oxygen bonds to carbon 3 on nucleotide 2 and the H2O remaining forms water. (COP) bond
which nitrogenous bases are complimentary pairs and how many hydrogen bonds form between them
adenine + thymine or uracil - 2 hydrogen bonds
guanine + cytosine - 3 hydrogen bonds
what are the 2 different types of nitrogenous base
purines - larger bases, made of double carbon ring structures (adenine and guanine)
pyrimidines - smaller one carbon ring structures (thymine, cytosine and uracil)
what are the monomers of DNA and RNA
DNA = nucleotides made from a pentose monosaccharide (deoxyribose), a phosphate group (phosphorus + 4 oxygens) bonded to carbon 5 on saccharide, and a nitrogenous base bonded to carbon 1 on saccharide
RNA = same as DNA but the pentose monosaccharide is ribose not deoxyribose
what are the 6 steps to DNA extraction from plant material
- grind a sample in mortar and pestle - breaks down cell walls
- mix sample with detergent - breaks down cell membrane releasing contents into the solution
- add salt - breaks hydrogen bonds between DNA and water molecules
- add protease enzyme - break down the proteins associated with the DNA in the nuclei
- add a layer of ethanol on top - alcohol causes the DNA to precipitate out of the solution
- the DNA will be seen as white strands - can be picked up by spooling it onto a glass rod
how is a double helix DNA chain formed
via hydrogen bonds between complimentary bases,
the two strands are antiparallel causing them to rotate around each other in opposite directions (the second strand must be turned upside down)
describe the semi-conservative process of DNA replication
(stages 1-9)
- takes place in nucleus
- double helix is UNTWISTED by the enzyme GYRASE
- HYDROGEN bonds are broken by the enzyme HELICASE
- each strand acts as a TEMPLATE for new molecule
- FREE DNA nucleotides in nucleus start to align with exposed strands
- COMPLIMENTARY base pairing (A-T) (G-C)
- HYDROGEN bonds form (A-T) 2 (G-C) 3
- covalent PHOSPHODIESTER bonds form between the phosphate of one nucleotide and the sugar of the other - using the enzyme DNA polymerase - makes sugar-phosphate backbones
- the results: 2 IDENTICAL STRANDS, each containing half the original DNA and half the new DNA
where does DNA replication take place
in the nucleus
what enzyme untwists the double helix in DNA replication
gyrase
what enzyme breaks the hydrogen bonds between the nitrogenous bases in nucleotides
helicase
what are the results of DNA replication
2 identical strands, each containing half the original DNA and half the new DNA
what stage does DNA replication occur in
the ‘s’ stage of interphase in the cell cycle
what are the 3 types of RNA molecules
mRNA - messenger
rRNA - ribosomal
tRNA - transfer
describe an mRNA molecule
copy of a template strand of DNA
has codons - 3 adjacent nucleotides that code for an amino acid
involved in transcription and translation
made in nucleolus and moves to ribosome as template for protein synthesis
describe the structure and functions of an rRNA molecule
complex molecule - accounts for half the mass of the ribosome (the rest is protein)
translation - takes place on ribosome (involves all 3 types of RNA)
describe the structure and functions of a tRNA molecule
small, single strand (around 80 nucleotides)
clover leaf shape
binding site for a specific amino acid
has an unpaired triplet of bases - anticodon
carries an amino acid to ribosome where it’s bonded to form a polypeptide
describe how transcription in protein synthesis is similar to DNA replication
the enzyme helicase unzips the DNA section
free nucleotides base pair
phosphodiester bonds form between the nucleotides
why does transcription occur in protein synthesis
because protein synthesis occurs outside the nucleus in the cytoplasm in the ribosomes. Chromosomal DNA molecules are too large to leave the nuclear envelope and supply coding information.
therefore, the base sequences of genes have to be copied (forming shorter molecules of RNA) and transported to the ribosome
describe how transcription in protein synthesis differs from DNA replication
gene is untwisted - small section of DNA not whole molecule
free RNA nucleotides complimentary base pair - not DNA
only one DNA strand is used as the template for mRNA
RNA polymerase catalyses formation of phosphodiester bonds - not DNA
mRNA is complimentary to template, not identical
describe the process of translation in protein synthesis
mRNA released from the nucleus through nuclear pore to the ribosome
mRNA binds to ribosome, a tRNA molecule attaches via its anticodon to the first codon of mRNA.
the tRNA is carrying a specific amino acid
multiple tRNA molecules bring the amino acids to the mRNA in the correct sequence (maximum of 2 at one time)
the ribosome moves along the mRNA chain, releasing the first tRNA molecule and repeating the sequence
at what point does translation stop
when the ribosome reaches the end of the mRNA at a stop codon and the polypeptide is released
what are the 3 rules of the genetic code
the genetic code is:
universal - all living organisms use the same code
degenerate - for most amino acids, there are more than one base triplet
non-overlapping - read starting from a fixed point in groups of 3
what are ADP and ATP composed of and why are they different?
both are phosphorylated nucleotides
both contain a pentose sugar - ribose
attached to a nitrogenous base - adenine
and either 2 or 3 phosphates
ADP - adenoside diphosphate = 2 phosphates
ATP - adenoside triphosphate = 3 phosphates
describe the hydrolysis of ATP
ATP + water –> ADP + Pi (inorganic phosphate) + energy
the energy is used by cells
(breaking the bond releases energy)
describe the condensation of ADP
ADP + Pi + energy (from glucose in food) –> ATP + H2O
(making the bond requires energy)
what bonds are broken during DNA replication?
hydrogen bonds between the bases
how many base pairs are there in one full turn of the DNA double helix
10
in a DNA sample, 20% of bases were adenine. what percentage were pyrimidines?
50%
20% thymine
30% cytosine
what technique was used to determine the double-helical structure of DNA?
X-ray crystallography
thymine comprised 36% of nitrogenous bases in a DNA sample, what percentage was guanine?
14%
T+A=72
C+G=28
C=G so 1/2x28= 14
what parts of the nucleotides contain carbon?
nitrogenous base and saccharide (not phosphate)
how many different trinucleotides can be made using the DNA nucleotides?
64 - 4 possible bases and 3 nucleotides so 4^3 =64
how many polynucleotide strands are found in a tRNA molecule?
1
What is the students t-test used for?
To determine whether 2 populations express significant or insignificant difference between population means
