Nucleic acids Flashcards
How many DNA Bases code for a single amino acid
3
How many different combinations of amino acids are there
4(3) - 64 combinations
What happens to the remaining combinations of amino acids
- several codons can code for one amino acid
- some used for start/stop/termination
- mutation results in a change in amino acid and a new one can easily be inserted
What is the definition of a gene
a gene is a section of DNA that codes for the production of a polypeptide
What is semi-conservative replication
One strand from original strand and one strand newly formed
Describe the process of transcription briefly
- DNA/ gene copied and transcribed into mRNA
- free activated (RNA) nucleotides
- line up by complimentary base pairing
- Catalysed by RNA polymerase
Describe briefly process of translation
- Mrna moves to ribosomes
- tRNA binds to mRNA
- anticodons bind to codons
- complimentary amino acid attaches to tRNA
- formation of peptide bond between amino acids
What is the importance of complimentary base pairing
- DNA can be replicated without error / same sequence of amino acids produced
- reduces occurrence of mutation
- allows formation of hydrogen bonds
How is the glucose molecule well suited to its function
- soluble so can easily be transported around the organism
- small - can easily diffuse across cell membranes
- easily broken down to release energy
- molecules can join alpha glucose molecules to form maltose (named disaccharides)
Describe the structural relationship between deoxyribose and the other components of the
DNA molecule.
- part of a nucleotide
- bonded to base and phosphate
- phosphate joined to C5/C3 base at C1
- part of backbone of DNA
- links to next phosphate on adjacent nucleotide
- nucleotide is a monomer of DNA
How does a DNA molecule replicate
- semi-conservative replication
- double helix unwinds
- hydrogen bonds between bases break
- each strand acts as a template for the formation of a new molecule
- free nucleotides align with exposed bases
- complimentary base pairing/ purine to pyrimidine
- hydrogen bonds reform
- sugar phosphate reforms /adjacent nucleotides join
- DNA polymerase joins backbone/strands
- each new molecule has one old strand and one new
How is information coded on genes is used to synthesis a polypeptide
- synthesis
- DNA, copied into /, mRNA or described ;
- transcription / transcribed ;
- one strand copied ;
- complementary base-pairing ;
- triplet code / code read in threes / codon is 3 bases ;
- base sequence determines amino acid sequence ;
- translation ;
- ribosomes ;
- role of tRNA described
How do polypeptides control the physical development of an organism
- haemoglobin e.g
- enzyme reactions/metabolism
- hormones
- receptors
- turning genes on/off
How does the structure of DNA allow it to function
-double stranded
-each strand acts as a template
-hydrogen binds easily break/form between bases
-complimentary base pairs
- purines can only pair with pyrimidines due to diff sizes giving equal sized rungs on the ladder
-Hydrogen bonding A-T = 2
C-G=3
What happens if the sequence of nucleotides change
- there is a different combination of amino acids
- different tertiary structure
- cant perform specific function
What supplies the energy for phosphodiester bonds
hydrolysis of activated nucleotides in the nucleoplasm
How to prokaryotes/mitochondria/chloroplasts replicate
- bubble sprouts
- unwinds/unzips
- complimentary bases join to exposed nucleotides
- eventually whole loop is copied
What is the complimentary base pairs
purines always pair with pyrimidines so rungs on the ladder are always the same length
Purines and pyrimidines
-purines - double ringed A+G
-Pyrimidines - single ringed - C+T
contains nitrogen
What is the difference between ribose and deoxyribose
deoxyribose contains an H instead of an OH
What is the meslston and Stahl experiement
proof of semi - conservative replication
1st - heavy as old DNA
2nd - 1X heavy 1x light
3rd- 1x hevay 2x light
semi conservative replication (in detail)
- DNA starts as a double helix, DNA gyrase - untwists
- DNA helicase unzips - breaks hydrogen bonds
- single stranded binding proteins attach to prevent reanneling (binding back together)
- DNA polymerase binds to the leadign strand and forms covalent phosphodiester bonds at the start of the replication fork
- moves in a 5’ 3’ direction
- free nucleotides in nucleoplasm fly in and attach via complimentary base pairs
- lagging strand synthesised discontinuously
- DNA ligase closes the gaps in the backbone
- each new strand consists of one old strand and one new
What does mRNA consist of
- contains ribose
- contains uracil
process of transcription (detail)
- gene unwinds/unzips
- hydrogen bonds break
- DNA polymerase catalyses the formation of temp hydrogen bonds between RNA and DNA bases on template strand
- coding strand produced complimentray to template strand
What are ribosomes made up of
- 2 subunits one large and one small
- protein and rRNA
What are the features of the genetic code
- universal - same in all organisms
- degenerate - multiple codes for one amino acid
process of transcription (detail)
- small subunit of rRNA binds to mRNA then large
- hydrogen bonds temporarily form
- tRNA binds to amino acids in cytoplasm which then is brought to mRNA
- complimentary base pairing between anti codon and codon
- peptide bonds from between two amino acids
- ribosmome moves along and a new tRNA comes in with anticodon
- peptide bond forms and continues till STOP codon is reached
Structure of tRNA
These tRNA molecules have a triplet of unpaired bases at one end (known as the anticodon) and a region where a specific amino acid can attach at the other
There are at least 20 different tRNA molecules, each with a specific anticodon and specific amino acid binding site
function of tRNA
The tRNA molecules bind with their specific amino acids (also in the cytoplasm) and bring them to the mRNA molecule on the ribosome
The triplet of bases (anticodon) on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule
Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying side by side
