Nucleotides And DNA Flashcards
What does a nucleotide consist of?
PENTOSE sugar
Nitrogen base
Phosphate group
What are the four bases?
Adenine
Cytosine
Guanine
Thymine
Components of RNA nucleotide?
Ribose sugar (Pentose) , with OH group (more susceptible to hydrolysis - makes a better transport molecule)
Phosphate group
1/4 bases
What are purines and pyrimidines?
PURINES : bases A and G - double ring structure
PYRIMIDINES : C and T - single ring structure
Purine can only pair with pyramidines due to size differences
How are nucleotides bonded together to form DNA/RNA ?
- joined tgt via condensation reactions
Condensation reaction occurs between PHOSPHATE GROUP and PENTOSE sugar - forms phosphodeister bond
What is the sugar phosphate backbone?
Chain of alternating phosphate groups and Pentose sugars , due to many phosphodister bonds
What is energy required for in living organisms ?
Anabolic reactions (building larger molecules from smaller molecules)
Moving substances across the cell membrane or moving substances within the cell
Muscle contraction– to coordinate movement at the whole-organism level
The conduction of nerve impulses
What is ATP?
energy-carrying molecule that provides the energy to drive many processes inside living cells
- type of nucleic acid
Ribose sugar , phosphate and base (adenine)
Adenosine nucleotide made when combined with 1, 2 and 3 phosphate groups?
1: AMP - adenosine monophosphate
2: ADP - adenosine diphosphate
3: ATP - adenosine triphosphate
Structure of DNA?
Made of 2 polynucleotide strands , running in opposite directions - ANTIPARALLEL (phosphodiester bonds link 5- carbon on sugar molecule to phosphate group on same molecule, which is also bonded to 3- carbon of sugar on next nucleotide)
THE POLYNUCLEOTIDE STRANDS made from deoxyribose sugars and phosphate groups bonded together (phosphodiester bond) to form the sugar - phosphate backbone
How are the bases held together in DNA?
A and T - 2 hydrogen bonds
G and C - 3 hydrogen bonds
What is semi conservative replication?
- occurs in preparation for mitosis as DNA molecules must be doubled before mitosis
1) enzyme helicase unwinds helix - breaks Hydrogen bonds between bases , so 2 single polynucleotide DNA stands made
2) these single strands act as a TEMPLATE for formation of new strand made from free nucleotides (attracted to exposed DNA bases)
3) new nucleotides are joined together by enzyme DNA POLYMERASE , catalysing condensation reaction between deoxyribose sugar and phosphate groups to form new strand - forms sugar-phosphate backbone on new DNA strand
- DNA polymerase breaks off 2 extra phosphate/use energy released to create phosphodiester bonds
4) original strand /new strand join tgt through hydrogen bonds between base pairs
What is a gene?
sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)
What does each sequence of 3 bases code for?
Sequence of Amino acids
What’s meant by a non overlapping genetic code?
Every base is only Read once
Why is the code degenerate?
64 different codons (triplets) but only 20 different amino acids - multiple codons can code for same amino acids
How is the genetic code universal?
Same triplet code codes for same amino acids in all living things
What is transcription ?
- hydrogen bonds between bases break and part of DNA unwinds - 2 separate strands
- One of the DNA strands is used as a template by RNA polymerase to make the mRNA molecule
- Free nucleotides line up by complementary base pairing
- adjacent nucleotides are joined by phosphodiester bonds made by RNA polymerase which moves along DNA - forms single stranded molecule of mRNA
- as RNA polymerase passes, the DNA strands reform their double helix structure
- mRNA then detaches from DNA TEMPLATE once stop codon is reached and moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm
What is translation?
- mRNA attaches to a ribosome and transfer RNA collects amino acids from the cytoplasm and carries them to the ribosome
- tRNA attaches itself to mRNA by complementary base pairing - 2 tRNA molecules attach to mRNA at once
- The amino acids attached to two tRNA molecules join by a peptide bond - formation is catalysed by rRNA and then tRNA molecules detach themselve, leaving them behind
• process repeated as ribosome moves along mRNA strand until stop codon reached leading to the formation of a polypeptide chain
Differences between dna replication and transcription
- in transcription, only small section of DNA unzips (where gene is located)
- from 2 daughter strands of DNA vs one strand of mRNA
- RNA /DNA free nucleotides
- DNA vs RNA polymerase
- different helicase enzymes
PRACTICAL: DNA purification
- Place the ethanol in a freezer 24 hours before starting the investigation
- Cut up the onion into small pieces (5 mm × 5 mm) - break down cell walls
- Add the washing-up liquid to 90 cm³ of tap water in a beaker
Add some of the onion pieces to the beaker - Place the beaker in a water bath at 60 °C for 15 minutes - detergent/high temp damages phospholipid bilayer releasing DNA
- Cool the mixture in an ice-water bath for 5 minutes, stirring it continually- lower temperature prevent breaking down if DNA
- Pour the mixture into a blender and blend for 5 seconds - breaks cell walls/membranes releasing more DNA
- Using the filter paper, filter the mixture into another beaker
- Pour 10 cm³ of the filtrate into a test tube and add 2-3 drops of protease enzyme, mixing well - removes proteins - leaves DNA
- Carefully add the ice-cold ethanol to the test tube and wait 2-3 minutes
Nucleic acids are insoluble in ice-cold ethanol and so the DNA forms a precipitate white layer) at the top of the test tube mixture
How is DNA and RNA different?
→ RNA contains ribose sugar
→ nucleotides in RNA form single polynucleotide strand
→ RNA contains uracil instead of thymine
What are histones and their function
- Histones are DNA-binding proteins.
DNA wraps around histones
Function : package DNA
Components of DNA nucleotides?
A deoxyribose sugar with hydrogen at the 2’ position
A phosphate group
One of four nitrogenous bases
