Nucleotides and nucleic acids Module 2 Flashcards
What’s a nucleotide made up of?
A pentose sugar (5 carbon atoms)
A nitrogenous base
A phosphate group
What elements do all nucleotides contain?
C, H O, N P
DNA and RNA are both types of?
Nucleic acid
What are the monomers of RNA and DNA?
Nucleotides
General purpose of DNA?
To store genetic information
General purpose of RNA?
To make proteins from the instructions in DNA
ADP and ATP are types of? and their function is?
Phosphorylated nucleotide
Store and transport energy in cells
What’s the pentose sugar in DNA called?
Deoxyribose
What are the 4 possible bases in DNA?
Adenine, thymine, cytosine, and guanine
Which are the purine bases and what does this mean?
Adenine and Guanine, contain 2 carbon - nitrogen rings joined together
Which are the pyrimidine bases and what does this mean?
Cytosine, and thymine, only contain 1 carbon-nitrogen ring, so are smaller than a purine base
How many polynucleotide chains does a molecule of DNA contain?
2
What’s the sugar in RNA called?
Ribose sugar
What does uracil (a pyrimidine) replace in RNA?
Thymine
How many polynucleotide chains make up RNA?
1
Structure of ADP?
Contains the base adenine, the sugar ribose and 2 phosphate groups
Structure of ATP?
Contains the base adenine, the sugar ribose, and 3 phosphate groups
Describe how ATP and ADP provide energy for a cell?
ATP provides energy for chemical reactions in a cell
It is synthesised from ADP and inorganic Pi, using the energy from an energy releasing reaction such as breakdown of glucose in respiration
So the ADP is phophorylated to from ATP and a phosphate bond is formed
Energy is stored in the phosphate bond, when the energy is needed by the cell, ATP is broken back down into ADP and Pi, and energy is released from the phosphate bond
What do nucleotides join together to form and what between?
Polynucleotides, phophodiester bond forms between the phosphate group of one nucleotide, and the sugar of another forming a sugar phosphate backbone
Describe how 2 polynucleotide strands join together to form a helix?
There’s hydrogen bonding between the bases
Complementary base pairing, A-T, C-G
2 Hydrogen bonds form between A-T
3 Hydrogen bonds form between C-G
The 2 antiparallel strands twist to form the DNA doubel helix
How can you purify DNA?
Via a precipitation reaction
Break up cells of sample using a blender
Make a solution of detergent, salt and distilled water
Add the broken up cells to a beaker containing the solution and heat in a water bath
The detergent in the mixture breaks down the cell membranes, and the salt binds to the DNA causing it to clump together, and warm temperature prevents the stops the enzymes in the cells working properly so DNA not broken down
Put beaker in a ice bath, and then filter
Transfer to a testube and protease enzymes to the filterered mixtures, which will break down any proteins
Dribble cold ethanol down side of tube so it forms a layer on top, causing DNA to form a white precipitate
Describe the process of DNA self replicating?
DNA helicase breaks down the hydrogen bonds between the 2 polynucleotide DNA strands, the helix unzips to form 2 separate strands
Each original strand acts as a template for a new strand, free floating DNA nucleotide bases join to the exposed bases on each original template strand by complementary base pairing
The nucleotides of the new strand are joined together by the enzyme DNA polymerase, this forms the sugar phosphate backbone,
Hydrogen bonds form between the bases on the original and new strand, the strands twist to form a double helix
Each new DNA molecule contains one strand from the original DNA molecule and one from new strand
Why is DNA self replication known as semi conservative?
Because half the strands are from the original DNA
What is a mutation and what might it cause?
Any change to the DNA base sequence, so may alter the sequence of amino acids a protein and therefore possibly form an abnormal protein
Why does DNA replication have to be very accurate?
So all the genetic information is conserved
What’s a gene?
A sequence of DNA nucleotides that codes for a polypeptide
The sequence of amino acids in a polypeptide forms the?
Primary structure of a protein
What determines the order of amino acids in a protein?
The order of nucleotide bases in a gene
Each amino acid is coded for by?
A sequence of 3 bases called a triplet in a gene
What is DNA copied in to and why for protein synthesis?
RNA
DNA molecules are found in the nucleus of the cell, but the ribosomes that make proteins are found outside the cell in the cytoplasm
DNA is too large to be moved out of the nucleus, so a section is copied into mRNA = transcription
So the mRNA leaves the nucleus and joins with a ribsome in the cytoplasm, where it can be used to synthesise a protein = translation
What are the 3 main types of RNA?
Messenger RNA - mRNA
Transfer RNA - tRNA
Ribosomal RNA - rRNA
Features of mRNA?
Made in the nucleus
3 adjacent bases are called a codon
It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s used to make protein during translation
Features of tRNA?
Found in the cytoplasm
It has amino acid binding site at one end, and a sequence of 3 bases called an anticodon
It carries the amino acids that are used to make proteins to the ribosome during translation
Features of rRNA?
Forms the 2 subunits in a ribosome
The ribosome moves along the mRNA strand during protein synthesis, the rRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids
What’s the genetic code?
The sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids
It’s non overlapping - read only in triplets
Degenerate - some amino acids are coded for by more than one base triplet
Universal - codes for same amino acids in all living thinfs
What are found at the beginning and end of gene to tell when to stop or start gene production?
Start/stop codons
Describe the first stage of protein synthesis - transcription?
RNA polymerase attaches to the DNA at the beginning of a gene
The hydrogen bonds break between the 2 DNA strands break, separating the strands, and the DNA molecule uncoils at that point
One of the strands is then used as a template to make an mRNA copy
The RNA polymerase lines up free RNA nucleotides alongside the template strand, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA strand (except T is replaced by U)
Once the RNA nucleotides have paired up with their specific bases on the DNA strand they are joined together to form an mRNA molecule
The RNA polymerase moves along the DNA, separating the strands, and assembling the mRNA strand
The hydrogen bonds reform between the uncoiled strands of DNA and coil back into a double helix once the RNA polmerase passes by
When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA
The mRNA moves out of the nucleus through a nuclear pore, and attaches to a ribosome in the cytoplasm
Describe how the second step of protein synthesis occurs Translation?
The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome
A tRNA molecule with it’s anticodon that’s complementary to the start codon on the mRNA attaches itself to the mRNA via complementary base pairing
A second tRNA molecule attaches to itself to the next codon in the same way
rRNA in the ribosomes catalyses the formation of a peptide bond between the 2 amino acids attached to the tRNA, this joins them together and the first tRNA molecule moves away
Process repeats untill a polypeptide chain is formed and the stop codon is reached
Order of protein synthesis?
Transcription then translation
