Module 2.1.3 Nucleotides Sambrook Flashcards
What are the purines in DNA?
Adenine
Guanine
DOUBLE ring structure
What are the Pyrimidines ?
Thymine
Cytosine
Uracil
SINGLE ring structure
Describe the structure of DNA
-DNA is made up of 2 complementary polynucleotide chains and the 2 strands are antiparallel.
-1 strand goes from 5’ to 3’ and the opposite strand goes from 3’ to 5’.
- hydrogen bonds hold the polynucleotide chains together.
- Ester bonds between the phosphate groups
- Hydrogen bonds between the nitrogenous bases
- this forms a double helix with major and minor grooves in an alternating pattern
What are nucleotides in DNA ?
-building blocks of DNA
-Made of a deoxyribose Pentosesugar molecule with hydrogen at 2’ position, phosphate group and a nitrogenous base.
-hold the genetic material of DNA
- deoxyribose
THYMINE
What is the significance of the nitrogenous base pairings in DNA ?
-Allows DNA to store and transmit genetic information.
-the specific pairing of the nitrogenous bases ensure that the genetic information is accurately copied during cell division.
How does DNA replication occur ?
-2 complementary strands of the DNA molecule separate
-each strand acts as a template for the formation of a new complementary strand.
How does the structure of DNA enable it to carry out its function?
1)Two strands = the DNA is stable
2)bases are inside the sugar phosphate back bone (spiral)= protected and the integrity of the genetic code is maintained
3)molecules are long = store a lot of genetic information
4) complementary base pairing = identical copies created
What are the components of RNA nucleotides?
-ribose pentose sugar with a hydroxyl group at the 2’ position (making is more susceptible to hydrolysis)
-URACIL
How many bonds are between adenine and thymine?
Two hydrogen bonds
How many bonds are between guanine and cytosine?
3 hydrogen bonds
What does helicase do?
(Step 1 of DNA replication)
-breaks down the hydrogen bonds between the 2 polynucleotide DNA strands.
-unzips helix.
What do we mean by semi-conservative?
One strand of the DNA is new and one is original
What direction does the leading strand go ?
3’ to 5’
What direction does the lagging strand go ?
5’ to 3’
What way does DNA polymerase move?
- in one direction
- 3’ to 5’
- on the original (template) strand
What are okazaki fragments?
- Short sequences of DNA nucleotides on the lagging strand.
-going in the wrong direction (away from the replication fork) so DNA polymerase synthasises the fragments in a discontinuous manner.
What does Ligase do ?
Put the okazaki fragments together
Stage one of DNA replication
1) DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands
The helix unzips to form 2 separate strands.
What is stage 2 of dna replication ?
2) each original strand acts as a template for the new free floating DNA nucleotides to attach h at the complementary nitrogenous bases
What is stage 3 of DNA replication?
3) DNA polymerase joins the nucleotides on the strands together
This forms a sugar phosphate backbone
Hydrogen bonds form between the nitrogenous bases on the new strands and original
What is stage 4 of DNA replication ?
4) strands twist to form a double helix
How do mutations occur ?
A change in the DNA base sequence
What can happen if a mutation occurs?
They can alter the sequence of amino acids in a protein
Causing an abnormal protein to be produced
What is genetic code non- overlapping?
Each codon ONLY codes for one amino acid
Base triplets don’t share their bases
Why is the generic code degenerate?
different codons can encode for the same amino acid
Why is genetic code universal?
All species use the same 4 nitrogenous bases
ATCG
each base codes for the same amino acid in all species
What is the Role of tRNA ?
-Carries the amino acids that are used to make proteins to the ribosomes
What is the role of mRNA?
-to deliver the genetic information from DNA to the ribosome to be translated into a protein
What is the role of rRNA?
-helps catalyse the information of peptide between amino acids
What is step one of transcription ?
1) rRNA polymerase attaches to the DNA at the beginning of a gene
The hydrogen bonds break separating the strands
The molecule uncoils with one of the strands being used as a template to make an mRNA copy
What is step two of transcription?
2) RNA polymerase lines up free RNA nucleotides along the template strand u
Complementary base paring means the mRNA strand ends up being a complementary copy of the DNA template (except T is U)
RNA nucleotides pair up with specific bases forming mRNA
What is the third stage of transcription?
3) RNA polymerase moves down the DNA, assembling the mRNA strand
The hydrogen bonds reform with RNA polymerase and the strands twist again
What is the fourth stage of transcription ?
4)RNA reaches a stop codon and stops producing mRNA and detaches itself from DNA moving out the nucleus through nuclear pores
Attached to the ribosome I’m the cytoplasm
What is the first stage of translation ?
1) tRNA carry amino acids to the ribosome
The codon on the mRNA attaches itself to an anticodon on the tRNA
What is the second stage of translation ?
2) the rNA in the ribosome catalyses the formation of a peptide bond between two amino acids
The first tRNA moves away lwaving the amino acid behind
This continues until a stop codon is reached on the mRNA molecule forming a polypeptide chain
What are nucleotides made of
-pentose sugar.
-nitrogenous base
-phosphate group
Elements: H,O,N and P
What is DNA nucleotide made up of?
-Penrose sugar -> deoxyribose
-phosphate group
-nitrogenous base -> GCAT
What is ADP made of?
-nitrogenous base -> adenine
-pentose sugar-> ribose
-TWO phosphate groups
What is ATP made of ?
-nitrogenous base ->adenine
-pentose sugar-> ribose
-THREE phosphate groups
Why does ATP and ADP have extra phosphate?
They have been phosphorylated
How is ATP made?
Phosphorylated from ADP + P and a phosphate bond is formed during a condensation reaction creating ATP and water
How is ATP released for use?
-energy is stored in phosphate bond
-ATP is broken back down into ADP and P
-energy is released from the phosphate bond
Describe Polynucleotide structure
-join from phosphate group of one nucleotide and sugar of another
-condensation reaction
-phosphodiester bond is formed -> phosphate group and 2 ester bonds
-chain -> sugar phosphate back bone
What reaction is used to purify DNA ?
Precipitate reaction
What does DNA do ?
-codes for sequence of amino acids in primary structure of protein determining its 3D structure
How to purify DNA using precipitation.
1) homogenise the cell with a detergent
2)filter to remove large debris
3) add salt to break hydrogen bonds between DNA and water molecules
4) add protease to digest the proteins
5) add ice-cold ethanol to precipitate the DNA out the solution (white strands)
What is a codon ?
-every 3 bases in the sequence that’s coded for an amino acid
Where is mRNA found?
-made in nucleus
-leaves into cytoplasm to go to ribosome
Where is tRNA found?
Cytoplasm
What is tRNA folded into ?
A clover leaf shape and bottom has 3 anticodons
When does DNA replication occur?
S - phase in interphase
