Nucleic Acids Flashcards
What does DNA stand for
Deoxyribonucleic acid
What is a nucleotide
Biological molecule consisting of a five-carbon sugar, a phosphate group and a nitrogenous base
what is the structure of a nucleotide
- phosphate esters of pentode sugars
- nitrogenous base is linked to C1 of the sugar
- phosphate group is linked to C5 of the sugar
- these are bonded by covalent bonds due to condensation reaction
When do nucleotides become phosphorylated nucleotides
When they contain more than one phosphate group
- ADP
- ATP
How are nucleotides able to help with metabolic pathways
- ATP
- ADP
- AMP
What is the structure of DNA
- polymer. Many repeated nucleotide units
- consist two polynucleotide strands
- two strands run in opposite directions (anti parallel)
- consist of a phosphate group, five carbon sugar (deoxyribose), one nitrogenous base
- nitrogenous bases: adenine, guanine, thymine, cytosine
- covalent bond between the sugar and phosphate group is called a phosphodiester bond
- phosphodiester bonds broken and formed when polynucleotides are synthesised
- long so can carry a lot of genetic coding
What is a purine
The nucleotide bases containing a double ring structure
what hydrogenous bases are purines
Guanine
Adenine
What is a pyramidine
Nucleotide base with one ring structure
What hydrogenous bases are pyramidine
Cytosine
Thymine
Uracil
What bonds are between hydrogenous pairs
Hydrogen bonds
How many hydrogen bonds are between adenine and thymine
2
How many hydrogen bonds are between guanine and cytosine
3
What gives DNA is helical structure
Purine is always paired with a pyrimidine.
- gives DNA ability to twist
What allows the DNA to unzip for transcription and replication
Hydrogen bonds
- weak
- easy to break
What part of the DNA is the 5’ end
The end of the molecule where the phosphate group is attached to the fifth carbon atom of the deoxyribose sugar
what part of the DNA is the 3’ end
Where the phosphate group is attached to the third carbon atom of the deoxyribose sugar
What do the rungs on the DNA ladder contain
Complementary base pairs
- joined by hydrogen bonds
What does the antiparallel sugar-phosphate backbone do for the integrity of the DNA
Allows the molecule to be very stable
- integrity of the coded information within the base sequences is protected
How is DNA organised in eukaryotic cells
- majority of DNA content is in the nucleus
- each large molecule of DNA is wound around special histone proteins into chromosomes
- each chromosome is one molecule of DNA
- loop of DNA inside mitochondria and chloroplasts
How is DNA organised in prokaryotic cells
- DNA is in a loop and is within the cytoplasm
- not wound around histone proteins
- described as naked
What is the structure of RNA
- pentose sugar (ribose)
- phosphate group
- nitrogenous base (uracil instead of thymine)
- one strand
- shorter strand
- either mRNA, tRNA or rRNA
What is the structure of ATP
- ribose
- adenine (nitrogenous base)
- 3 inorganic phosphates (phosphate group)
What is semi-conservative replication
How DNA replicated
- results in two new molecules
- each containing one old strand and one new strand
- one old strand is conserved in each new molecule
How does a DNA molecule split into two
Unwinds - the double helix untwists, a little at a time, catalysed by a gyrase enzyme
Unzips - hydrogen bonds between nucleotide bases are broken. catalysed by DNA HELICASE. This results in two single strands of DNA with exposed nucleotide bases
What happens after the DNA has been separated
- free nucleotides, in the nucleoplasm, bond to the exposed bases. Using complementary base pairings
- DNA POLYMERASE catalyses the addition of new bases from 5’ to 3’. DNA zips back together
- leading strand is synthesised continuously
- lagging strand is synthesised in fragments (discontinuous)
- these fragments are then joined together by ligase
What are the steps of DNA replication
- unwinds
- unzips
- bases attach
- zips back up
How can mutations occur in replication
The wrong nucleotide may be inserted
- could change the genetic code (point mutation)
What is a gene variation
Different variations of a particular gene
What are the five main feature of genetic code
- triplet code
- non overlapping
- degenerate
- universal
- determines amino acid sequence
What is triplet code in genetic code
- three bases (codon) code for an amino acid
- the three complementary bases on tRNA form an anticodon
- triplet codons for ‘start’ and ‘stop’ signals
What does it mean when genetic code is non-overlapping
All of the codons are separate
What does it mean when genetic code in degenerate
Most amino acids have more than one code
What does it mean that genetic code is universal
All life on earth has the same DNA code for amino acids
What does it mean by genetic code can determine amino acid sequences
DNA codes for RNA, this in turn codes for proteins
The proteins produced then form and regulate all other processes
Examples of the primary structure of a polynucleotide being correct
- shape of the active site must be complementary to the substrate
- part of an antibody must have a complementary shape to the antigen on the surface of an invading pathogen
- receptor of a cell membrane must have a complementary shape to the cell signalling molecule that it must detect
- ion channel protein must have hydrophilic amino acids lining the outside of the channel
What is translation
The process of making mRNA from a DNA template
What is translation
Formation of a protein, at ribosomes, by assembling amino acids into a particular sequence according to the coded instructions carried from DNA to the ribosomes by mRNA
What are the steps of transcription
- gene unwinds and unzips
- hydrogen bonds break
- RNA POLYMERASE allows nucleotides to bond to their complementary bases
- length of RNA that is complementary to the template strand is produced
- this forms coding strand
- mRNA passes out nucleus and attaches to a ribosome
What does the large subunit of ribosomes contain in translation
3 binding site
- E
- P
- A
What happens at the A site
Where tRNA enters ribosome
- holds tRNA carrying the next amino acid to be added to the polypeptide chain
What happens at the P site
Holds tRNA carrying the growing polypeptide chain
- where the codon and anticodon bind
- condensation reaction forms peptide bonds between amino acids
What happens at the E site
Where the tRNA exits the ribosome
- site from which tRNA that has lost its amino acid is discharged
What are the main steps of translation
- small subunit of ribosome attaches to mRNA
- tRNA attaches to mRNA
- large subunit of ribosome attached around tRNA on mRNA
- tRNA enters A site
- polypeptide chain starts to grow
- tRNA leaves E site
- process continues
- release factor enters A site
- all elements are released resulting in a polypeptide chain
What happens inside the large subunit of ribosome
- anticodon of tRNA attaches to codon of mRNA
- polypeptide chain is formed
What does the mRNA carry in translation
The nucleotide code for the protein to be made
What does tRNA do in translation
Interpret the molecule code
- each tRNA carries an amino acid and an anticodon
What is the structure of tRNA
Clover structure
- D arm
- T arm
- anti codon
- acceptor stem (amino acid)
What are the processed of protein synthesis
- DNA unzips: DNA helicase
- DNA polymerase bonds adjacent nucleotides
- hydrogen bonds form and helix returns
- pre mRNA leaves through nuclear pores
- turn into mature mRNA with splicing
- tRNA brings amino acid into ribosome subunit (A site)
- codon and anticodon bind (P site)
- polypeptide chain grows
- tRNA leaves ribosome (E site)
- amino acid binds to tRNA (tRNA activation)
What is splicing
The process by which introns, no coding regions of genes, are taken out of the mRNA transcript. Exons, coding regions, are joined together to make mature mRNA
