TOPIC 3: NUCLEOTIDES AND NUCLEIC ACIDS Flashcards
NUCLEOTIDES:
What is the structure of DNA nucleotides?
-DNA is a molecule which has a double helix structure
-This means it contains two polynucleotide chains bonded together by hydrogen bond between the nitrogenous bases
- The two chains/ trads are anti-parrallel to each other
- All DNA nucleotides have a pentose sugar called deoxyribose / same phosphate group but the nitrogenous base can be different ( A,T,C,G )
NUCLEOTIDES:
What is the structure of RNA nucleotides and its various roles?
as messenger RNA which synthesised during transcription (mRNA)
- RNA is a single stranded molecule - it is only one polynucleotide chain = single helix
- All RNA nucleotides have a pentose sugar called ribose / the same phosphate group but the nitrogenous base can be different ( A,U,C,G)
RNA has various roles:
# bringing specific amino acids as transfer RNA in translation (tRNA)
# the site for protein synthesis - ribosomes (rRNA)
NUCLEOTIDES:
What is the properties of nucleotides?
- A type of biological molecule
- Made from : a pentose sugar, a nitrogenous base, and a phosphate group
- All nucleotides contain the elements C,H,O,N and P
- DNA and RNA are found in all living cells
- DNA is used to store gentic information
- RNA is used to make proteins from the instructions in DNA
POLYNUCLEOTIDES AND DNA:
What is the structure of polynucleotides
- Nucleotides join together to form polynucleotides
- Formed by condensation reactions of nucleotides
- The bond which forms is called a phosphodiester bond and is found between the phophate group of one nucleotide and the pentose sugar of another»_space; forms the sugar- phosphate backbone
- Hydrolysis of this phosphodiester bond produces the monomers,nucleotides
- Purines always bonds with a pyrimidine
- The hydrogen bonds make DNA a very strong and stable strucure which helps limit the number of mistakes/ mutations in the gentic instructions
NUCLEOTIDES:
What are the differences and similarities between purines and pyrimidines?
Purine has a 2-carbon-nitrogen ring = larger
Pyrimidines has a 1-carbon-nitrogen ring = smaller
They are both bases
NUCLEOTIDES:
Which bases go with purines and pyrimidines?
Purines - Adenine and Guanine
Pyrimidines - Cytosine, Thymine, Uracil
NUCLEOTIDES:
Why do purines only bind to pyrimidines?
To preserve DNA dimensions
NUCLEOTIDES:
What is the structure of ATP and ADP?
ATP:
- These are phosphorylated nucleotides
- Contains the base adenine
- The sugar ribose
- Three phosphate groups
ADP:
- To phosphorylate a nucleotide, you add one or more phosphate group by a condensation reaction
- Contains a base adenine
- The sugar ribose
- Two phosphate groups
NUCLEOTIDES:
What is the properties of ATP?
Small- can be moved easily
Water soluable cells have aqueous environment
Contains unstable bonds between phosphates - lots of energy released
Releases energy in small quantities - efficient so minimise waste
Easily regenerated - renewable energy source
NUCLEOTIDES:
Where is ATP produced?
Produced in the mitrochondira by respiration
POLYNUCLEOTIDES AND DNA:
What is the structure of DNA?
- DNA is composed of two polynucleotides strands joined together to form a double-helix shape
- The two strands joined together by hydrogen bonding between bases
- Complementary base pairing bewteen A-T and C-G
- 2 hydrogen bonds between A-T and 3 hydrogen bonds between C-G
- The two polynucleotide strands are antiparallel –> which twist to form the double helix
DNA REPLICATION:
What is DNA replication and why does DNA replicate?
It is when DNA copies itself before cell division so that each new cell has the full amount of DNA
Important for passing genetic information and making new cells
DNA REPLICATION:
How is DNA replicated?
1) DNA helicase ( an enzyme ) breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzip to form single strand
2) Each original strand acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing > A-T and C-G
3) The nucleotides on the new strand are joined together by the enzyme DNA polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds between the bases on the original and new strand.
The strand twist to form a double helix. Each new DNA molecule contains one strand from the original DNA molecule and one new strand.
DNA REPLICATION:
What is DNA replication called and why?
- Semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA
DNA REPLICATION:
What happens if a randon, spontaneous mutation occurs ?
A mutation isn’t a change to the DNA base sequence
Mutations = can alter the sequence of amino acids in a protein
Can cause abnormal protein to be produced.
TRANSCRIPTION AND TRANSLATION:
What is the process of transcription?
1) RNA polymerase attches to the DNA
- Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene
- The hydrogen bonds between the two DNA strands, and the DNA molecule uncoils at that point
- One of the strands is then used as a template to make an mRNA copy
2) Complementary mRNA is formed
- The RNA polymerase lines up free RNA nucleotides alongside the template strands
- Complementary base pairing means that the mRNA strands ends up being a complementary copy of the DNA template strand (except the base T is replaced by U in RNA)
- Once the RNA nucleotides have paired up with their specific bases on the DNA strand they’re joined together, forming an mRNA molecule.
3) RNA polymerase moves down the DNA strand
- The RNA polymerase moves along the DNA, seperating the strands and assembling the mRNA strand
- The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double helix
4) mRNA leaves the nucleus
- When RNA polymerase reached a stop coden, it stops making mRNA and detaches from the DNA
- The mRNA moves out nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage takes place
TRANSCRIPTION AND TRANSLATION:
Where does translation take place?
Takes place in the ribosomes in the cytoplasm
TRANSCRIPTION AND TRANSLATION:
What happens during translation?
Amino acids are joined together by a ribosme to make a polypeptide chain, following the sequence of codons carried by the mRNA
TRANSCRIPTION AND TRANSLATION:
What is the process of translation?
1) The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosmes
2) A tRNA molecule, with an anticoden that’s complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing
A second mRNA molecule attaches itself to the next codon on the mRNA in the same way
3) rRNA in the ribosome catalyses the formation of a peptide bond between the two amino attached to the tRNA molecules. This joins the amino acids together
The first tRNA molecule moves away, leaving its amino acid behind
4) A third tRNA molecule binds to the next codon on the mRNA
Its amino acids binds to the first two and the second tRNA molecule moves away
This process continues, producing a chain of linked amino acids, until there’s a stop codon on the mRNA molecule
- The polypeptide chain ( protein ) then moves away from the ribosome and translation is complete
GENES AND PROTEIN SYNTHESIS:
What is a gene?
A sequence of DNA nucleotides that codes for a polypeptide
TRANSCRIPTION AND TRANSLATION:
What is translation?
When the mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein
TRANSCRIPTION AND TRANSLATION:
What is transcription?
When DNA is too large to move out of the nucleus, so a section is copied into mRNA
DNA REPLICATION:
What is the role of the enzyme DNA helicase?
An enzyme that unwinds the double helix by breaking the hydrogen bonds between the complementary bases
DNA REPLICATION:
What is the role of the enzyme DNA polymerase?
Free nucleotides form hydrogen bonds with the exposed complementary bases
DNA polymerase create polynucleotide chains by catalysing phosphodiester bonds
Essential for DNA replication, and usually works in pairs, to create two identical DNA strands, each containing one original DNA strand
DNA REPLICATION:
What is the role of the enzyme DNA ligase?
Facilitates the joining of the DNA fragments together by catalysing the formation of phosphodiester bonds
Described as “stealing nicks” in the sugar phosphate backbone to form a continuos strands of DNA
GENES AND PROTEIN SYNTHESIS:
What is RNA?
Single stranded molecule - single helix
All RNA nucleotides have a pentose sugar called ribose the same phosphate group but the nitrogenous base can be different ( A,U,C,G )
GENES AND PROTEIN SYNTHESIS:
What is messenger RNA (mRNA) ?
Single polynucleotide strand
Made in the nucleus during transcription
mRNA carries the gentic code from the DNA in the nucleus to the cytoplasm, where it’s used to make a protein during translation
In mRNA, groups of three adjacent bases are called codons
GENES AND PROTEIN SYNTHESIS:
What is transfer RNA (tRNA) ?
tRNA is a single polynucleotide strand that’s folded into a clover shape
Hydrogen bonds between specific base pairs hold the molecule in this shape
Every tRNA molecule has a specific sequence of three bases at one end called anticodon
They also have an amino acid binding site at the other end
tRNA is found in the cytoplasm where it’s involved in translation
Carries the amino acids that are used to make proteins to the ribosomes
GENES AND PROTEIN SYNTHESIS:
What is ribosomal RNA (rRNA)?
rRNA forms the two subunits in a ribosome, along with proteins
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
GENES AND PROTEIN SYNTHESIS:
What is the gentic code?
It is the sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids
In the genetic code, each base triplet is read in sequence, seperate from the triplet before it and after it
Base triplets don’t share their bases - the code is non-overlapping
GENES AND PROTEIN SYNTHESIS:
What is the universal code?
When the gentic code has the same specific base triplets code for the same amino acids in all living things
GENES AND PROTEIN SYNTHESIS:
What is the degenerate code?
Multiple codons can code for the same amino acids
The degenerate nature of the gentic code can limit the effect of mutations
