Module 2: Topic 2:3: Nucleotides and Nucleic Acids. Flashcards

Question

Describe the process of DNA replication.

Answer 1

1) DNA helicase unwinds the double helix, this breaks the hydrogen bonds between complementary base pairs to separate the strands. one of the strands will act as a template for synthesis of the other strand. 2) Complementary nucleotides will attach to the template strand by hydrogen bonding. DNA polymerase then catalyses the formation of phosphodiester bonds between nucleotides, forming a complementary strand alongside the template parent strand. Two daughter DNA molecules are formed, each containing half of the original DNA double helix.

Answer 2

DNA polymerase must accurately copy the template strand to avoid placing the wrong DNA nucleotide in the wrong position. To avoid this, DNA polymerase proof reads the complementary strand as it moves along the DNA and if it detects a mismatch, it can ship out the wrong nucleotide and replace it with the right one. It has an accuracy rate of 99%. This means that mistakes do occur every once in a while.

Answer 3

A mutation is a change to the DNA base sequence. A DNA mutation can have detrimental effects to the organism, since an altered base sequence can change the sequence of amino acids in a protein, causing it to fold differently and possibly lose its function.

Answer 4

Messenger RNA - mRNA Transfer RNA - tRNA Ribosomal RNA - rRNA

Answer 5

It is a single polynucleotide strand and it contains uracil as a base instead of thymine.

Answer 6

It is a single polynucleotide strand and is produced during transcription. It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it is used to make a protein in translation. Groups of three adjacent bases are called codons.

Answer 7

It is a single polynucleotide strand that is folded into a clover shape. It carries amino acids to the ribosomes during translation. It contains an amino acid binding site at one end and an anti-codon at the opposite end. It is found in the cytoplasm where it is involved in translation. It carries the amino acids that are used to make proteins to the ribosomes.

Answer 8

It associates with proteins to form two subunits that make up the ribosome. The ribosome moves along mRNA during protein synthesis. The rRNA in the ribosome helps to catalyse the formation of peptide bonds between amino acids.

Answer 9

It is three nucleotide bases that make up a codon, which codes for a particular amino acid.

Answer 10

The codons do not overlap. Once the ribosome has 'read' one codon, the ribosome will move onto the next.

Answer 11

This is the idea that all organisms use the same genetic code.

Answer 12

The genetic code 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 a sequence, separate from the triplet before it and after it- base triplets do not share their bases, they are non-over lapping. The genetic code is degenerate - different codons can code for the same amino acid. For example, the codons CUU and CUC both code for the amino acid leucine. This means that some mutations will have no effect on the organism since the same protein will still be produced.

Answer 13

No. Some triplets are used to tell a cell when to stop the production of a protein. these are called STOP SIGNALS. They are found at the end of mRNA

Answer 14

Transcription and Translation.

Answer 15

1) The enzyme RNA polymerase attaches to the DNA double helix. The hydrogen bonds between the two DNA strands break, separating the strands. The DNA double helix uncoils and one of the strands is used as a template to make an mRNA copy. 2) The RNA polymerase lines up free floating RNA nucleotides alongside the template strand. Complementary base pairing occurs through the formation of phosphodiester bonds. Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they are joined together by RNA polymerase, forming an mRNA strand. 3) The RNA polymerase moves along the DNA, assembling the mRNA strand. The hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double helix. 4) When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA. The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where Translation will next take place.

Answer 16

This process takes place at the ribosomes in the cytoplasm. The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome. A tRNA molecule, with an anticodon that is complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way. rRNA in the ribosome catalyses the formation of the peptide bond between the two amino acids attached to the tRNA molecules. this joins the amino acids together. The first tRNA molecule moves away, leaving its amino acid behind. A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away. The process continues, producing a chain of linked amino acids, until there is a stop codon on the mRNA molecule. The polypeptide chain, protein, then moves away from the ribosome and translation is complete.