P1CC1 Chapter 5 - Nucleic Acids and Their Functions Flashcards
What are the monomers of nucleic acids?
Nucleotides
State the three components of nucleotides.
Pentose Sugar
Organic Base
Phosphate Group
How does the structure of a nucleotide look?
Phosphate group – 5 Carbon Sugar – Nitrogenous Base
What are the two types of organic base?
Purine and Pyramidine
What is a purine?
- A class of organic structures
- Has a double ring structure
- Includes Adenine and Guanine
What is a pyramidine?
- A class of organic bases
- Single ring structure
- Includes Thymine, Cytosine and Uracil
Describe the sturcture of a DNA nucleotide.
- Deoxyribose sugar
- Organic Base (A,T,C,G)
- Phosphate Group
Describe the structure of an RNA nucleotide.
- Ribose sugar
- Organic base (A,T,C,G)
- Phosphate Group
Describe the structure of an ATP nucleotide.
- Ribose sugar
- Adenine
- Three phosphate groups
What is an endergonic reaction?
A non-spontaneous reaction that requires an input of energy, Eg: ATP formation.
What is an exergonic reaction?
A spontaneous reaction that overall releases energy, eg: ATP Hydrolysis
Describe the role of ATP.
The universal energy currency. Hydrolysed to release energy.
ATP + Water <–> ADP + Pi + Energy
What is complementary base pairing?
Describes how hydrogen bonds form between complimentary purine and pyramidine bases.
Two bonds between A and T (or U)
Three bonds between C and G
Describe the structure of DNA. (4)
- Double stranded polymer of nucleotides twisted to form a double helix.
- Nucleotides joined together by phosphodiester bonds
- Hydrogen bonds form between complementary base pairs, A and T, C and G.
- Antiparallel Strands
Why are the strands of a DNA double helix described as ‘antiparallel’?
The complimentary strands run parallel but in opposite directions. 5’ to 3’ and 3’ to 5’.
Describe the structure of RNA. (3)
- Single stranded polymer of nucleotides
- Nucleotides joined together by phosphodiester bonds
- Hydrogen bonds form between complementary base pairs, A and U, C and G.
Compare and contrast DNA and RNA.
DNA vs RNA:
1. Double Stranded vs Single Stranded
2. Long Chain of Nucleotides vs Shorter chain of nucleotides
3. Contains deoxyribose sugar vs Contains ribose sugar
4. Contains bases A,T,C and G vs Contains bases A,U,C, and G
5. Storage of genetic information vs Role in protein synthesis
6. Phosphodiester bonds join nucleotides vs Phosphodiester bonds join nucleotides.
Name the three types of RNA found in cells.
- tRNA = Transfer RNA
- mRNA = Messenger RNA
- rRNA = Ribosomal RNA
What is the function of tRNA?
It carries specific amino acids to the ribosomes.
Describe the structure of tRNA. (4)
80 nucleotides
Single helix
Clover leaf shape
Anticodon on one end, amino acid binding site on the other
What is the function of mRNA?
Carries genetic information from the nucleus to the ribosomes for protein synthesis.
Describe the structure of mRNA.
2000 nucleotides
Single helix
Unstable
What is the function of rRNA?
Associates with proteins in the cytoplasm to form ribosomes.
Describe the structure of rRNA.
1800 - 5000 nucleotides
Two subunits: One large, One small
What is semiconservative replication?
The replication of DNA to produce two new DNA molecules which both contain one new strand and one old strand from the original DNA molecule.
What is the role of DNA Helicase in semiconservative replication?
Catalyses the unzipping of double-stranded DNA into two single strands, each of which acts as a template.
What is the role of DNA Polymerase in semiconservative replication?
It catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.
What is the genetic code? (collection of exons)
The rules where triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain. The genetic code is known as degenerate, universal and non-overlapping.
Why is the genetic code described as degenerate?
More than one triplet can code for a particular amino acid.
Why is the genetic code described as universal?
The same codons code for the same amino acids in almost all organisms.
What is meant by ‘non-overlapping’?
Each base in a sequence is read once and is only part of one triplet.
Describe the ‘triplet code’ for amino acids.
A specific sequence of three nucleotides (known as codon) on a molecule of DNA or RNA coding for a particular amino acid in protein synthesis.
What is an exon?
A region of DNA that CODES for an amino acid sequence.
What is an intron?
A non-coding sequence of DNA that is found between exons.
Compare eukaryotic and prokaryotic genes.
Eukaryotic genes are discontinuous with non-coding introns and coding exons.
Prokaryotic genes are continuous with coding sequences only.
What is protein synthesis?
The formation of protein from amino acids. There are two stages, transcription and translation.
Define transcription.
- The first stage of protein synthesis
- The formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA.
Outline the process of transcription.
- DNA helicase unwinds section of DNA, breaking hydrogen bonds between DNA strands. Antisense strand acts as a template.
- RNA Polymerase binds to the promoter region of a gene
- Free RNA Nucleotides align next to their complimentary bases.
- RNA Polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds.
- RNA Polymerase reaches stop codon and detaches. mRNA is complete.
Describe post-transcriptional modification.
Splicing removes introns from pre-mRNA in eukaryotic cells.
Define translation.
- The second stage of protein synthesis
- Takes place in ribosomes
- mRNA used as a template for attachment of rRNA molcuiles with complementary anticodons. Amino acids carried on the adjacent tRNA molecules are joined to form a polypeptide chain.
Outline the process of translation.
- mRNA attaches to groove between subunits of ribosome.
- Ribosome moves along mRNA until ‘start codon’ reached.
- Amino acid-tRNA complex anticodon attaches to the complementary mRNA codon via hydrogen bonding. Another complex binds.
- Peptide bond forms between adjacent amino acids in the complex.
- Ribosome moves along one codon and releases the empty tRNA. Process continues to form polypeptide chain until ‘stop’ codon is reached.
What is the ‘one gene - one polypeptide’ hypothesis?
The theory that each gene encodes a single protein.
What happens to the polypeptide after translation?
It is further modified by adding carbohydrates, lipids or phosphates.
Different polypeptides may be combined.
Describe how DNA can be purified by precipitation.
Add ethanol and a salt to aqueous solution. Nucleic acids precipitate out of solution.
Centrifuge to obtain pellet of nucleic acid.
Wash pellet with ethanol and centrifuge again.
