8.4 - Protein synthesis: transcription and splicing

Question 1

what is the basic process for how he cytoplasm manufactures proteins

Answer 1

• DNA provides the instructions in the form of a long sequence of bases
• A complementary section of part of this sequence is made in the form of a molecule called pre-mRNA (transcription)
• the pre-mRNA is spliced to form mRNA
• the mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide - process called translation (translation)

Question 2

link the process of the cytoplasm creating different types of proteins, to baking

Answer 2

• equipment + oven = cell organelles
• cake created = proteins
• ingredients = amino acids
• the recipe = genetic code
• recipe book = genome
• making a photocopy of a recipe to use in the bakery = transcription
• making cakes with the photocopied recipe = translation

Question 3

what is transcription

Answer 3

the process of making pre-mRNA using part of the DNA as a template

Question 4

describe the process of transcription

Answer 4

• semi-conservative model but then instead of DNA polymerase…
• RNA polymerase moves along the strand and joins he nucleotides together to form a pre mRNA molecule
• A-U and C-G
• as the RNA polymerase adds the nucleotides one at a time to build a strand of pre-mRNA the DNA strands re-join behind it = only 12 base pairs on the DNA are exposed at any one time
• when the RNA polymerase reaches a particular sequence of bases on the DNA that it recognises as a ‘stop’ triplet code, it detaches, and the production of pre-mRNA is then complete

Question 5

where does transcription result from in prokaryotic cells

Answer 5

results directly in the production of mRNA from DNA

Question 6

where does transcription result from in eukaryotic cells

Answer 6

results in the production of pre-mRNA, which is then spliced to form mRNA

Question 7

describe the DNA of a gene eukaryotic cell

Answer 7

• made up of sections called exons
  –> they code for proteins and sections (called introns) that don’t
  –> these intervening introns prevent the synthesis of a polypeptide – therefore need to be spliced

Question 8

describe the splicing of pre-mRNA

Answer 8

• inside them: the base sequence corresponding to the introns are removed and the functional exons are joined together
• not necessary in Prokaryotic cells (most don’t have introns)
• once mRNA molecules have been spliced they leave via a nuclear pore (too big to diffuse out of nucleus)
• once left, outside the nucleus: the mRNA is attracted to the ribosomes to which it becomes attached, ready for the next stage of the process (translation)