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Flashcards in Genetic control of protein Deck (24)
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Why is the transcribed mRNA strand shorter than the DNA template strand? (2)

  • Introns are present in DNA.
  • This is the non-coding part


Differences in structure between mRNA and tRNA (8)

mRNA vs tRNA::

  • Linear and longer vs Clover leaf shape but shorter
  • No binding site for amino acid vs Binding site present 
  • No H bonds vs H bonds present between nucleotides
  • No anticodon region vs Anticodon region



Describe the role of tRNA in translation (3)

  • anticodon must be complementary to codon for tRNA to read the message on mRNA
  • tRNA carries specific amino acid to ribosome
  • amino acids combine using ATP to form polypeptide;


Starting with mRNA in the nucleus, describe of protein is synthesised (8)

  1. mRNA leaves the nucleus through nuclear pore
  2.  and goes to ribosome in the cytoplasm
  3. tRNA molecules bring amino acids to ribosome
  4. specific tRNA molecule for specific amino acid;
  5. anticodon of tRNA must be complementary to codon on mRNA;
  6. using ATP, peptide bonds form between amino acids;
  7. tRNA detaches and collects another amino acid;
  8. ribosome moves along mRNA;


Role of RNA polymerase (1)

  • By forming phosodiester bonds, it attaches nucleotides, to form a mRNA strand
  • checks and corrects mismatched base pairs


Examples of mutagenic agents 

  • uv light 
  • tobacco tar


Describe how an altered gene results in a different colour pigment in a plant. Enzymes involved (4)

  • sequence of bases in mRNA would change;
  • amino acids sequence different so different 1• structure
  • this affects hydrogen bond formation
  • so changes tertiary structure of enzyme so its  active sites are changed
  • relevant substrates can't bind


Explain why the DNA base sequences of homologous chromosomes are almost the same (3)

  • Homologous chromosomes have same genes;
  • At the same loci;
  • Different alleles usually have only a small differences in base sequence;


Describe how a new protein is made once a gene has been inserted into a cell (8)

  • Unzipping of DNA by breaking hydrogen bonds;
  • DNA helicase does this
  • RNA nucleotides are attached by complementary base pairing 
  • RNA polymerase is used to make pre mRNA strand ;
  • pre mRNA is spliced, removing introns
  • mRNA enters ribosomes;
  • Specific tRNA molecule associated with specific amino acid;
  • Anticodon must be complementary to mRNA;
  • Amino acids join by formation of peptide bonds;
  • ATP is used to provide energy to do this;
  • The gene has now been switched on;


Describe transcription (4)

  1. DNA helicase cause the DNA strands separate;
  2. The exposed strand acts as a template
  3. Free nucleotides bind to one strand by complementary base pairing (U-A) (G-C)
  4. RNA polymerase joins nucleotides to form pre mRNA;


Describe the features of a gene which enable it to code for a particular protein (8)

  • Gene is a section of DNA which consists of a sequence of bases
  • code read in threes;
  • Triplet codes for 1 amino acid, which combine to form a polypeptide;
  • Degenerate code;
  • non-overlapping;
  • start/stop codes present;


Differences and similarites between DNA and RNA (7)

Similarities :

  • both have phosphate
  • AGC in common 
  • pentose sugar;


  • DNA has deoxyribose whereas RNA has ribose;
  • DNA thymine, RNA Uracil
  • DNA double stranded, RNA single stranded;
  • DNA longer;
  • Only one type DNA, RNA 3 types: mRNA,tRNA, rRNA


Differences and similarites between DNA replication and transcription (8)


  • DNA acts as template;
  • Both involve polymerase enzyme;
  • Complementary base pairing


  • All of DNA is copied whereas only a section copied in transcription ;
  • one strand used transcription, two in replication;
  • enzymes that are different, D(R)NA polymerase


Why is only 1% of our genetic information transcribed into functional RNA sequences? (4)

  • Only some genes switched on;
  • different proteins and enzyme are required by different cells;
  • some DNA does not codes (introns)
  • Repeated DNA (stutter sequences)


Describe the structure of tRNA (4)

  • Consists of 1 polynucleotide
  • Hydrogen bonds are present inbetween the bases
  • Anticodon region
  • Amino acid attachment region
  • Clover shape


Why does addition and deletion result in an non-functional protein being formed? 

  • A nucleotide is added or deleted
  • Causes frame shift
  • DNA triplets after point of mutation are altered
  • so mRNA codons after point of mutation altered
  • Different sequence of amino acids in polypeptide so primary structure different;
  • this affects hydrogen bond formation
  • Alters tertiary structure of protein




Degenerate code definition (1)

  • One amino acid can be coded for by more than one triplet;


Define codon (2)

  • 3 bases on DNA;
  • That code for an amino acid;


Explain why knowing the DNA sequence of exons, but not introns is useful in ascertaining mutations (4)

  1. Introns not translated 
  2. Exons code for amino acids
  3. Mutations of exons affect amino acid sequences;
  4. This leads to a change in tertiary structure so a faulty protein is made


Why are the proportions of bases in the middle section of a chromosome different to that of the end

  • Different genes;
  • Have different base sequences 


Even though the base sequence changes, why can the same amino acid sequence be the same

  • 1. Genetic code degenerate;
  • 2. Mutation in intron;


Why does a mutation of a tumour suppressor gene result in a tumour

  • Tumour suppressor gene inactivated
  • So not able to control cell division
  • Rate of cell division too fast


How can smoking cause tumours

  • Contains carcinogens which causes mutation;
  • Of genes controlling cell division;
  • Tumour suppressor genes inactivate;
  • Causes protooncogenes to mutate into oncogenes;
  • Leads to uncontrolled cell division


What is a transcription factor?

1. Protein that moves from cytoplasm to DNA;

2. and binds to promoter;

3. which leads to mRNA production