Answers to DNA replication protein synthesis worksheet by M6Fyt1u


									B3.3 Genetics                                                                ANSWERS

Worksheet Two                                                   Molecular Genetics 1

  1. Nucleotide drawn and labelled showing deoxyribose sugar, nitrogenous base and
     phosphate group.

     A section of DNA drawn showing the nucleotides running anti-parallel.

  2. Nucleotides are asymmetrical. This is based on the numbering of the carbon
     atoms. The 5’carbon joins to the phosphate group while the 3’ carbon joins to the
     next nucleotide. When they are joined together to form DNA, the DNA has a
     direction. For base pairing to occur on the opposite side of the DNA, the direction
     runs in the opposite direction giving an antiparallel structure, i.e.
                  3’             5’
                  5’             3’

  3. Enzymes e.g. helicase etc
     Structural e.g. hair
     Hormones e.g. insulin
     Immune system e.g. antibodies

  4. This refers to the flow of information from DNA to mRNA to protein.
5. Proteins primary structure is the sequence of amino acids. This is then folded into
   either pleated sheet or an alpha helix shape due to hydrogen bonds to form the
   secondary structure. The tertiary structure occurs when attraction between the
   alpha helix and the pleated sheet structures forms a globular shape. The
   quaternary structure occurs if more than one amino acid chain is present.

6. To make an identical copy of the DNA for cell division.

7. Diagram shows DNA replication occuring with the following features: helicase,
   replication fork, DNA ligase, DNA polymerase, leading strand, lagging strand,
   okazaki fragments.

8. a)    The replication fork is the point where the DNA is unzipped by helicase to
   enable free nucleotides to be attached to the parent strand by the enzyme DNA
   polymerase to make identical copies.

   b)    Nucleotides can only be attached to the template strand in the 5’ to 3’
   direction. Therefore on the lagging strand the nucleotides are added in small
   sections, called Okazaki fragments, as the DNA is unzipped and joined together
   later by DNA ligase.

   c)    As DNA runs antiparallel the leading strand runs from the 5’ direction to
   the 3’ direction meaning nucleotides can be added continuously. The lagging
   strand is the opposite (3’ to 5’) so the nucleotides form Okazaki fragments.

9. Because the process creates two identical strands of DNA each consisting of one
   of the original strands and one newly synthesised strand.
10.   Both DNA and RNA consist of repeating units of nucleotides with the bases A, G
      and C. However, DNA has T and RNA has U. DNA nucleotides have a
      deoxyribose sugar and RNA has a ribose sugar. RNA is shorter and has a variety
      of forms and functions e.g. tRNA, mRNA and rRNA. DNA is double stranded
      (double helix) and more stable than RNA.

11.   A codon is a series of three nucleotides on mRNA that is complementary to a
      triplet on the coding strand of DNA. Whereas an anticodon is complementary to
      the codon and is found on the tRNA.

12.   Transcription is the process of copying the DNA code by making mRNA. This is
      done by the DNA unwinding and unzipping. The enzyme RNA polymerase
      attaches free RNA nucleotides by complementary base pairing to the coding
      strand of DNA to produce mRNA. This then leaves the nucleus for translation to

13.   Both processes involve making a copy of the DNA code in the nucleus.
      Transcription makes a copy of the code by producing mRNA with RNA
      nucleotides. Whereas DNA replication uses DNA nucleotides to produce an
      identical copy. DNA replication uses both sides of the DNA, whereas
      transcription only uses the coding strand. The enzymes are also different; DNA
      replication uses helicase, DNA polymerase and DNA ligase, whereas
      transcription uses RNA polymerase.

14.   Degeneracy refers to the fact that there is more than one codon for each amino
      acid. This is an advantage because if there is a mutation (a change in the sequence
      of bases) then there is a chance that there would be no effect to the sequence of
      amino acids in the protein.
15.      Translation is the process where a protein is formed from mRNA. mRNA moves
         into the cytoplasm where tRNA brings the complementary amino acid. These are
         joined with peptide bonds to form a polypeptide chain and eventually a protein.


               Enzyme                    Process(es)                Role
      Helicase                     DNA replication        Unwinds and unzips the
      DNA polymerase               DNA replication        Attaches DNA
                                                          nucleotides to DNA
      RNA polymerase               Transcription          Attaches RNA
                                                          nucleotides to DNA
      DNA ligase                   DNA replication        Joins Okazaki
                                                          fragments together


      Anticodon         A sequence of three nucleotides in a transfer RNA (tRNA),
                        that codes for an amino acid.
      Central Dogma     The transcription of DNA to RNA and then translated into a
      Coding Strand     The strand of DNA that has the complementary sequence to
      Codon             Sequence of three mRNA nucleotides coding for one amino
      Complementary The specific pairing of base A with T and base C with G in
      base pairing      double-stranded DNA.
      Disulphide        Bond between two sulfur-containing amino acids in a folded
      Bridge            protein chain.
DNA Ligase       An enzyme involved in the DNA synthesis and repair. Its
                 function is to join the fragments of DNA together, e.g.
                 Okazaki fragments.
DNA              An enzyme that adds bases to a replicating DNA strand.
Duplication      A part of the chromosome is present in two or more copies.
Helicase         An enzyme that unwinds and unzips the DNA helix.
Lagging Strand   The strand of DNA that is synthesised discontinuously during
                 replication (because DNA synthesis can proceed only in the 5´
                 to 3´ direction).
Leading Strand   The strand of DNA that is synthesised continuously during
mRNA             (messenger RNA) RNA species that contains the information
                 to specify the amino acid sequence of proteins and that is
                 translated on the ribosome.
Nucleotide       A building block of DNA or RNA, consisting of one
                 nitrogenous base, one phosphate molecule, and one sugar
                 molecule (deoxyribose in DNA, ribose in RNA).
Okazaki          An Okazaki fragment is a relatively short fragment of DNA
Fragment         created on the lagging strand during DNA replication.
Protein          The formation of a specific protein. Individual amino acids are
Synthesis        joined together in a specific sequence, determined by an
                 mRNA molecule.
Purines          One of two families of nitrogenous bases found in nucleotides.
                 Two members are adenine and guanine.
Pyrimidines      One of two families of nitrogenous bases found in nucleotides.
                 Three members are cytosine, thymine and uracil.
Replication     The replication fork is a structure that forms within the
Fork            nucleus during DNA replication. It is created by helicases,
                which break the hydrogen bonds holding the two DNA strands
RNA             An enzyme which helps synthesize mRNA by transcribing the
Polymerase      nucleotide sequence in DNA.
Template        The strand of the DNA double helix that is transcribed by
Strand          complementarily base pairing to make an mRNA.
Transcription   The synthesis of mRNA copy from a sequence of DNA (a
                gene); the first step in gene expression.
Translation     The synthesis of a protein using mRNA code.
Triplet         A sequence of three nucleotides on the template DNA strand.
                Each triplet represents the code for a particular amino acid.
tRNA            A type of RNA molecule that carries a specific amino acid
                and matches it to its corresponding codon on an mRNA during

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