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What is a gene and what is the relatioship between a gene, a protein and an enzyme
A gene is a basic unit of heredity in a living organism.
It is a stretch of DNA which contains all the DNA triplets needed to produce a specific protein.
It is located at a specific site on a chromosome
Explain what is meant by the term DNA template
A DNA template is the specific combination of nucleotide bases which can be copied during transcriptions
Describe the roles of the 3 main types of RNA:
Messenger RNA
Transcribes DNA code and carries it from the nucleus to the cytoplasm
Carries genetic information from DNA in the nucleus to the ribosomes for protein synthesis
Describe the roles of the 3 main types of RNA:
Ribosomal RNA
In the cytoplasm, rRNA and protein combine to form a ribosome. The ribosome attaches itself to the mRNA and prodives the stabilising structures to hold all substance in position which translation occurs
Describe the roles of the 3 main types of RNA:
Transfer RNA
Contain about 75 nucleotides, three of which make an anti-codon; each anti-codon codes for 1 amino acid. tRNA reads the mRNA sequence of codons and translates the information to find the appropriate anti-codon for the codon which occurs

Brings amino acids to the ribosomes for protein synthesis
DNA contains the nitrogen bases:
RNA contains the nitrogen bases:
Define the terms:
Transcription takes place in the nucleus when the DNA code is copied and a complementary strand of mRNA is created
Define the terms:
Translation occurs in the sytoplasm and involves the mRNA attaching to a robosome, and tRNA reading the code, to ultimately develop a polypeptide chain
Explain the importance of hydrogen bonding between bases in:
Hydrogen bonds are weak.
They are present in DNA so that during the process of transcription, the DNA can be easily unzipped and copied.
Explain the importance of hydrogen bonding between bases in:
Hydrogen bonds are important in translation because bonds between the anti-codons and amino acids need to break to allow polypeptide chain to form
Explain the significance of the weak hydrogen bonds between bases (compared to the stronger covalent bonds) in protein synthesis
H bonds are used because little energy is required to break these bonds compared to the amount of energy that would have to be expended to break a stonger covalent bond.
Describe the role of the enzyme RNA-polymerase in the formation of mRNA
RNA polymerase is the enzyme which makes the exposed DNA code 'sticky' and promotes hydrogen bonding between the DNA and the complementary nucleotide
Describe how information required for protein synthesis is transferred from DNA in the nucleus to the cytoplasm
Once the information has been copied and edited into exons (more concise strand), the mRNA leaves the nucleus through a nuclear pore and enters the cytoplasm of the cell
Describe the role of ribosomes in protein synthesis
During protein synthesis, complete ribosomes are make up of two sub units. The small ribosomal subunit initially nestles the nRNA strand.
Once the codon had bound with it complimentary anti-codon, the large ribosomal subunit interlocks with the small one and they hold the mRNA strand in place which tRNA anti-codons attach to the binding sites between the subunits of the ribosome
Triplet Codon
Sequence of three nucleotides whcih ultimately code for an amino acid
A section of mRNA made up of three nucleotides which complements DNA sequence
A section of tRNA made up of three nucleotides which codes for an amino acid
Describe the structure of t-RNA in terms of:
It's overall architecture
It is a small RNA molecule. It's secondary structure is like a clover, with an amino acid attachment side and an anti-codon opposite it. Tertiary structure has an L-shape
Describe the structure of t-RNA in terms of:
The site for attachment of an amino acid
Is a tail from the clover shaped molecule
Describe the structure of t-RNA in terms of:
The unpaired base triplet (anti-codon)
Made up of three nucleotides (C, G, A, U)
Explain the attraction between tRNA and the specific amino acids, in terms of reactive sites
tRNA anti-codons code specifically for one of 20 amino acids.
The reactive site will only connect with their complimentary amino acid
Describe the main steps involved in the translation of the message contained in mRNA into a polypeptide chain at the ribosome
  • mRNA leaves the nucleus through a nuclear pore and enters the cytoplasm
  • Here, a small ribosomal subunit holds the mRNA stand and a start codon attaches to it, holding methamine
  • Then a large ribosomal subunit attaches to the complex, becoming a complete ribosome
  • A tRNA then 'reads' the mRNA strand and attaches a complimentary anti codon and in turn another amino acid. This amino acid binds with the adjacent one and the anti codon is released from the ribosome
  • This continues until a stop codon is reached and a polypeptide chain has been formed
Describe the importance of the polyribosome in the production of protein molecules
Polyribosomes are very important during the process of translation
They hold the mRNA molecule in place and provide active site in which polypeptide chain can be formed
Predict the possible effects on a cell if a mistake is made during protein synthesis
  • The mistake could result in no change in the cell as correct amino acid is still coded for by different nucleotide
  • It could result in death of the cell as it is no longer able to function appropriately
  • Improvement in the cell, it becomes faster at synthesis through use of different amino acid
Describe the possible effects on cellular structure and function of a change in the DNA code for a gene
If the DNA code changes, this could result in no change or mutation (positive or negative)
Why is controlling of protein synthesis crucial to controlling a cells structure and function?
The structure and functions of a cell are all a result of protein structures.
If the synthesis of proteins was not controlled, the cell would have different characteristics and function in a different manner
Describe the regulation of protein synthesis in terms of gene induction and repression by hormones and other messengers
Protein synthesis is regulated by induction and repression depending on the cells requirements for proteins
Explain the term:
Gene expression
Gene is switched on/activated so that its functional product is produces
Explain the term:
Gene repression
Gene is switched off/prevented from being transcribed by blocking of RNA polymerase
Explain why only some genes in a cell are never expressed
Not all genes in a cell are expressed because the proteins they code for may not be required
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