2.1.3 - Nucleotides and nucleic acids Flashcards
1
Q
What is the monomer of nucleic acids?
A
- Nucleotides
2
Q
Structure of a nucleotide
A
- Phosphate group : Acidic and negatively charged
- Pentose sugar
- Nitrogenous base
3
Q
RNA vs DNA
A
Sugar: Ribose vs Deoxyribose
Bases: A,C,G,U vs A,C,G,T
Polynucleotide chains : 1 vs 2
Chain length : Short chain(can leave the nucleus) vs Short chain(can leave the nucleus)
4
Q
Purines and pyrimidines
A
- Purine : Two carbon rings ( Adenine and Guanine)
- Pyrimidines : One carbon ring ( Thymine and cytosine)
- A smaller base always binds to a larger base, this arrangement maintains a constant distance between phosphates
5
Q
Synthesis of polynucleotides
A
- Polynucleotides are synthesised through condensation reactions
- Nucleotides react to produce polynucleotide and water
- The phosphate group on the fifth carbon of the pentose sugar of one nucleotide forms a covalent bond with the hydroxyl group in the third carbon of the pentose sugar of an adjacent nucleotide. These bonds are called phosphodiester bonds
- This forms a long, strong sugar-phosphate backbone
6
Q
Breakdown of polynucleotides
A
- Polynucleotides are broken down by hydrolysis reaction
- Water has to be added for the reaction to take place
- The phosphodiester bonds are broken
7
Q
DNA
A
- Nucleotide monomers: Phosphate group, deoxyribose sugar, nitrogenous base.
- It consists of two strands of polynucleotides
- The two strands are coiled into a double helix.
- The hydrogen bonds between complementary base pairs hold the two strands together
8
Q
Anti parallel
A
- Each strand has a phosphate group(5’) at one end and a hydroxyl group(3’) at the other end
- The two strands are anti-parallel as the two parallel strands are arranged so that they run in opposite directions
9
Q
DNA nucleotides
A
- Nucleotides can have one of four of bases: adenine, cytosine, guanine, thymine.
- Complementary base pairing is the specific hydrogen bonding between nucleic acid bases
- Adenine binds to Thymine : 2 hydrogen bonds
- Cytosine binds to Guanine : 3 hydrogen bonds
- DNA has an equal amount of adenine & thymine and cytosine & guanine
10
Q
Purifying DNA by precipitation
A
- Sample grinded : To break the cell wall
- Sample mixed with detergent : This breaks down the cell wall releasing the cell contents into solution
- Add salt : This breaks the hydrogen bonds between DNA and water molecules
- Add protease enzyme : Breaks down proteins associated with the DNA in the nuclei
- Add layer of alcohol : Alcohol causes DNA to precipitate out of solution
11
Q
DNA Extraction buffer
A
- Detergent
- Salts
- Protease enzyme
12
Q
DNA replication
A
- The enzyme helicase causes the two strands to unzip and separate. It breaks the hydrogen bonds between complementary base pairs
- Helicase finishes the separation of the strand. At the same time free nucleotides attach to their complementary base pairs.
- DNA polymerase forms phosphodiester bonds between nucleotides. It only travels in the 3’ to 5’ direction, so only the leading strand can be replicated continuously.
- The lagging strand cannot be made continuously because the replication fork and polymerase run in opposite directions. DNA polymerase will therefore bond them in small sections, called Okazaki fragments. Ligase enzyme bonds all the fragments.
13
Q
Semi- conservative replication
A
- One strand is from the original DNA and the other strand is newly formed
- The original strand acts as a template for the new strand
14
Q
ATP
A
- Adenine
- Ribose sugar
- 3 inorganic phosphate
15
Q
ADP
A
- Adenine
- Ribose sugar
- 2 inorganic phosphate
16
Q
Energy
A
- Energy is the ability to do work
- Energy is needed for:
- > Synthesis
- > Transport
- > Movement
17
Q
How ATP releases energy?
A
- Energy needed to break bonds
- Energy released when bonds form
- Small amount of energy required to break the weak bond holding the last phosphate group in ATP
- A large amount of energy is then released when the phosphate undergoes other reactions.
18
Q
ATP hydrolysis
A
ATP + H2O -> ADP + Pi + Energy
19
Q
How ATP is synthesised?
A
Phosphorylation
- Phosphorylation is a condensation reaction where an inorganic phosphate group is reattached to an ADP molecule
20
Q
Properties of ATP
A
- Small: Moves easily into and out of cells
- Water soluble: Energy requiring processes happen in aqueous solutions
- Instant source of energy
- Releases energy in small amounts as needed
- Easily regenerated : Can be recharged with energy
21
Q
Meselson and Stahl
A
- Tube with generation 0 : Parent DNA, Only heavy nitrogen N15
- Tube with generation 1: It is a hybrid contains light nitrogen N14 and heavy nitrogen N15.
- Tube with generation 10: Highest band gets thicker because more of DNA made from only N14.
22
Q
Mutations
A
- A mutation is a change in the genetic material which may affect the phenotype of the organism.
- Sequence of bases may be copied incorrectly
- These changes occur randomly and spontaneously
23
Q
Triplet code
A
- Sequence of three nucleic acid bases, called a codon.
- Each codon codes for one amino acid
24
Q
Non-overlapping
A
- Adjacent codons don’t overlap
- No single base takes part in the formation of more than one codon.
- One codon signals the start of the sequence
- It prevents errors in the amino acid sequence
25
Universal
- All organisms use the same genetic code
| - Only the sequence of bases coding for each individual protein will be different
26
Degenerate
- Degenerate means that more than one codon codes for one amino acid
- 64= 4x4x4
- Multiple codons code for the same amino acids, there are also start and stop codons
- Having multiple codons coding for one amino acid means if one base in the mRNA is copied correctly it could still code for the correct amino acid.
27
Transcription (What it does?)
DNA is transcribed into mRNA
28
Transcription (Where?)
Nucleus
29
Transcription (What happens?)
1. The DNA unwinds and unzips
2. The antisense strands act as the template strand
3. Free RNA nucleotides line up by complementary base pairs
4. RNA polymerase forms phosphodiester bonds between the RNA nucleotides
5. mRNA detaches and leaves the nucleus through the nuclear pore
6. DNA winds back up
30
Translation ( What it does? )
Polypeptide is formed
31
Translation (Where?)
Ribosome
32
Translation (What happens?)
1. mRNA moves to ribosome
2. tRNA anti codons bind to mRNA codons
3. Specific amino acids are attached to the tRNA, amino acids are brought together in the correct sequence
4. Peptide bonds form between amino acids
33
State the number of nucleotide bases that code for one amino acid
3
34
There is a maximum of 64 different base combinations in DNA that could each code for an amino acid.
How is this number of combinations calculated?
4x4x4
35
Twenty different amino acids are commonly used for protein synthesis. In theory, this would need only 20 different base combinations.
Explain the uses of the remaining 44 combinations
- Multiple codons code for one amino acid
- Some are used as start or stop codons
- A mutation in the sequence may not lead to a change in the amino acid
36
Which nucleotide bases are common to DNA and RNA?
Adenine
Cytosine
Guanine
37
Describe how a nucleotide base sequence in a gene is used to synthesis a polypeptide
TRANSCRIPTION
- DNA transcribed into mRNA
- Free RNA nucleotides
- line up by complementary base pairs
- on template strand
- RNA polymerase bonds them together
TRANSLATION
- mRNA moves to ribosomes
- tRNA molecules bind to mRNA
- Anticodons bind to codons
- Specific amino acids attach to tRNA
- Peptide bonds form between amino acids
38
Explain why complementary base pairing is important in DNA replication
- DNA can be replicated without error, same sequence of nucleotides is produced
- Reduces occurrence of mutation
- Allows reformation of hydrogen bonds
39
Suggest why DNA molecule is unable to leave the nucleus
- It consists of two strands, so it is too big
| - It cannot fit through the pores in the nuclear envelope.
40
Explain why mRNA molecule is shorter than DNA molecule
- mRNA only copies one gene or part of DNA
| - mRNA codes for 1 protein, DNA codes for multiple proteins.
41
State what a gene codes for
Polypeptide
42
Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for
- Different sequence of amino acids
- Protein folds up differently
- Different function or can no longer function
43
Explain how the structure of DNA allows replication
- Double stranded
- Both strands act as template
- Hydrogen bonds easily break and form between bases
- Complementary base pairing
- Purine only binds to pyrimidine
- 3 H bonds C&G
- 2 H bonds A&T
44
State the role of mRNA
carries / transfers, the (complementary DNA) ,
out of the nucleus ;
(transfers it) to the, ribosome / RER / site of translation ;
for, protein / polypeptide, synthesis ;
45
What technique was used to determine the double helical structure of DNA?
X-ray crystallography
