Chapter 3 - Nucleotides and Nucleic Acids Flashcards
What are the two types of nucleic acids?
DNA and RNA
What is a nucleotide made up of?
5 Carbon deoxyribose sugar
Nitrogenous base
Phosphate group
What is a nucleic acid?
A large polymer formed from many nucleotides linked together in a chain
How are nucleotides linked together?
Condensation reaction
Phosphodiester bond between the phosphate group of one nucleotide and the hydroxyl group of the sugar
What does DNA stand for?
Deoxyribonucleic acid
What are the five different nitrogenous bases?
Adenine (A), Guanine (G), Cytosine (C) and Thymine (T), Uracine (U)
What is a pyrimidine?
The smaller bases which contain single carbon rings (Thymine and Cytosine)
What is a purine?
The larger bases which contain double carbon rings structures (Adenine and Guanine)
Which bases bond with each other and with how many hydrogen bonds?
Thymine and Adenine (2 Hydrogen bonds)
Cytosine and Guanine (3 Hydrogen bonds)
What two enzymes are involved in DNA replication?
Helicase and polymerase
What does helicase do?
Unwinds the double helix and separates the two strands
What does polymerase do?
Builds the new strand by forming new phosphodiester bonds between nucleotides
How do mutations occur?
If a base sequence is not matched correctly
Describe DNA
Double stranded molecule that forms a double helix
Nucleotide that holds genetic information
Strands are anti-parallel running in opposite directions
Describe the structure of an RNA nucleotide
Ribose sugar
Phosphate group
Nitrogenous bases
Describe RNA
Short single stranded molecule used on protein synthesis
What are nucleotides?
Monomers which form nucleic acids; like DNA and RNA
Which nitrogenous bases are complementary to each other in DNA?
Thymine and Adenine
Guanine and Cytosine
(Always a purine and pyrimidine base paired together)
Which nitrogenous bases are complementary to each other in RNA?
Uracil and Adenine
Guanine and Cytosine
(Always a purine and pyrimidine base paired together)
Why is it important for a purine and pyrimidine to pair together?
To help maintain the order of the genetic code when DNA replicates
What is ATP?
Adenine triphosphate
Composed of adenine, ribose and 3 inorganic phosphate groups
Why is ATP important?
Essential for metabolism
3 phosphate ions play significant role in energy transfer
Immediate source of energy for biological processes
How is ATP formed?
Made during respiration via a condensation reaction using ATP synthase
ADP + Pi -> ATP + H2O
Pi = inorganic phosphate group
How is ATP broken down?
Hydrolysed using ATP hydrolase
ATP + H2O -> ADP + Pi
Releases small amount of energy breaking the bond between one of the phosphate groups
Pi = inorganic phosphate group
What is ADP?
Adenine diphosphate
How does DNA structure relate to its function?
Stable structure - due to sugar-phosphate backbone and the double helix
Double stranded - easy replication using opposite strand as a template
Weak hydrogen bonds between bases - low energy required to separate the strands during replication
Large molecule - carries a lot of information
Complimentary bases - allows identical copies to be made
What are the three types of RNA?
mRNA - messenger RNA
tRNA - transfer RNA
rRNA - ribosomal RNA
What is rRNA?
Main bulk of ribosome structure
What is mRNA?
Copy of one gene from DNA
Created in nucleus, leaves via nuclear pore which is carried to a ribosome in cytoplasm or RER
Shorter than DNA
Short-lived (can be easily broken down by enzymes in cytoplasm)
Single stranded and every 3 bases code for an amino acid (codons)
What is tRNA?
Found in cytoplasm
Single stranded but folded to create clover leaf shape held in place by hydrogen bonds
Brings specific amino acids to ribosomes
Determined by the 3 bases found on the tRNA (anticodon) which are complimentary to 3 bases on the mRNA (codon)
Why is DNA replication described as semi-conservative?
One strand is conserved and a new strand is created
When in the cell cycle does DNA replication occur?
S-phase in interphase
What are the stages of DNA replication?
- DNA helicase beaks the hydrogen bonds between the complimentary bases to unwind the double helix and the strands separate
- Both strands act as templates for DNA replication
- Free-floating DNA nucleotides align opposite their complementary base on the template stand of DNA. Hydrogen bonds form between base pairs
- DNA polymerase joins adjacent DNA nucleotides together, forming a phosphodiester bond between these nucleotides to create a new polymer chain of DNA
What are the main features of the genetic code?
Degenerate
Universal
Non-overlapping
What is meant by degenerate in the genetic code?
Amino acids are coded for by more than one triplet of bases
What is meant by universal in the genetic code?
The same triplet of bases codes for the same amino acid in all organisms
What is meant by non-overlapping in the genetic code?
Each base in a gene is only part of one triplet of bases that codes for one amino acid. Each codon, or triplet of bases, is read as a discrete unit.
What are the two stages of protein synthesis?
Transcription - where the DNA sequence for one gene is copied into mRNA
Translation - where the mRNA joins with a ribosome and a corresponding tRNA molecule brings the specific amino acid the codon codes for
What are introns?
Sequences of bases in a gene that do not code for amino acids and therefore polypeptide chains. These get removed, spliced, out of mRNA molecules after transcription
What are exons?
Sequences of bases in a gene that code for a sequence of amino acids
What is a start codon?
At the start of every gene
Allows ribosomes to attach
Initiates translation
What is a stop codon?
At the end of every gene
3 bases that do not code for an amino acid
Causes ribosome to detach and ends translation
What is the process of transcription?
DNA helicase breaks down hydrogen bonds between bases in the two strands of DNA
DNA helix unwinds - one strand acts as a template
Free mRNA nucleotides align opposite exposed complementary DNA bases
RNA polymerase joins together the adjacent RNA nucleotides, forming phosphodiester bonds - creates new mRNA polymer chain
Once gene is copied, mRNA is modified and leaves the nucleus through the pores
What is the process of translation?
mRNA attaches to the small subunit of the ribosome at the start codon
tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA (two tRNA molecules can fit in at once)
Two amino acids get delivered by the tRNA molecule, which join together via peptide bonds which is catalysed by an enzyme using ATP
Ribosome moves along the mRNA molecule to the next codon and another complementary tRNA will attach to the next codon on the mRNA
Ribosome continues until the stop codon so the ribosome detaches
A polypeptide chain is now formed and will enter Golgi body for folding and modification
