2.3 Nucleotides and Nucleic acids Flashcards
What is the DNA backbone made up of?
Phosphate molecule bonded to pentose sugar bonded to a nitrogenous base
Which bonds are formed between bases?
Hydrogen bonds
What does DNA stand for?
Deoxyribonucleic acid
What is the difference between RNA and DNA?
The Thymine base is changes to U (Uracil)
What is a purine?
Guanine and Adenine
They have a double ring structure
What is a pyrimidine?
Thymine and Cytosol
They have a single ring structure
What bond is formed between nucleotides?
A phosphodiester bond
How do bases pair up?
A — T
C — G
How is DNA copied?
Via semi-conservative replication
What does semi-conservative replication mean?
In each new DNA molecule produced, one of the polynucleotide DNA strands is from the original DNA molecule being copied
The other polynucleotide DNA strand (the other half of the new DNA molecule) has to be newly created by the cell
Therefore, the new DNA molecule has conserved half of the original DNA and then used this to create a new strand
Why does one original DNA strand need to be retained?
Retaining one original DNA strand ensures there is genetic continuity (i.e. genetic information is conserved) between generations of cells
What are the stage of Semi-Conservative replication?
- helicase unwinds the DNA double helix by breaking the hydrogen bonds bases on the two antiparallel polynucleotide DNA strands form two single polynucleotide DNA strands
- Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing
- new nucleotides are then joined together by the enzyme DNA polymerase which catalyses condensation reactions to form a new strand
What is a gene?
a sequence of nucleotides that forms part of a DNA molecule
What is the triplet code?
The sequence of DNA nucleotide bases found within a gene is determined by a triplet (three-letter) code
Each sequence of three bases (i.e. each triplet of bases) in a gene codes for one amino acid
What is meant by non-overlapping code?
Each base is only read once in which codon it is part of
What is degenerate code?
Where multiple codons can code for the same amino acids
What is meant by universal code?
Almost every organism uses the same code - the same 4 bases (there are a few rare and minor exceptions)
What is a codon and an anti-codon?
Each triplet within the mRNA code is described as a codon
The tRNA molecules that transfer amino acids possess anticodons which are complementary to the codons on mRNA
What are the stages of protein synthesis?
- Transcription
—> DNA is transcribed and mRNA molecule is produced - Translation
—> mRNA is translated and an amino acid sequence produced
What are the stages in transcription?
Occurs in the nucleus:
1. The DNA molecule unzips around the gene - the sense strand - via DNA helicase
2. The template strand (antisense strand) allows a complementary base strand of RNA to be formed which has the same base sequence as the sense strand
3. RNA polymerase pairs the free complementary RNA base pairs up with the exposed bases on the antisense strand - forms mRNA .
4. mRNA leaves the nucleus through a nuclear pore
5. the original DNA strand double helix reforms
What are the stages of Translation?
- mRNA from transcription travels to a ribosome in the cytoplasm
- the ribosome reads the mRNA, and a molecule of tRNA leave to find the complementary amino acid to the base sequence on mRNA
3.
What is the role of RNA Polymerase?
Synthesises RNA by following a strand of DNA.
What is the role of mRNA?
Carries the base sequence from DNA in the nucleus to ribosomes
What is the role of tRNA?
Contains an anticodon which has complementary codon on mRNA
What is the role of rRNA?
