the different processes

Question 1

describe the process of transcription

Answer 1

1 - the enzyme RNA polymerase moves along the DNA, unwinding the double helix and breaking the hydrogen bonds between the bases
2 - RNA polymerase synthesises a primary transcript of mRNA from free RNA nucleotides by complementary base pairing
3 - RNA polymerase keeps adding nucleotides from the 5’ end to the 3’ end of the growing mRNA molecule until a specific sequence of nucleotides called a STOP codon is reached. the resulting mRNA strand separates and is now called a primary trandscript of mRNA.

Question 2

describe the process of splicing and alternative RNA splicing

Answer 2

splicing:
RNA splicing forms a mature mRNA transcript. the introns of the primary transcript are non-coding regions and are removed. the exams are coding regions and are spliced together to form the mature transcripy. the order of the exons is unchanged during splicing.

alternative RNA splicing:
the same gene can be used to make several different proteins by treating different regions as introns and exons. this means the same primary mRNA transcript has the potential to produce several mature mRNA transcripts depending on which exons are retained.

Question 3

describe the process of translation

Answer 3

1 - the mature mRNA transcript attaches to a ribosome in the cytoplasm
2 - the start codon begins protein synthesis
3 - complementary tRNA anticodons attach to the mRNA strand, bringing a specific amino acid to form the protein molecule
4 - peptide bonds join the amino acid molecules. each tRNA molecule leaves the ribosome once the amino accids are attached.
5 - a stop codon ends protein synthesis

Question 4

describe the process of DNA replication

Answer 4

1 - prior to cell division, DNA is replicated by a DNA polymerase.
2 - DNA is unwound and hydrogen bonds between bases are broken to form two template strands.
3 - DNA polymerase adds DNA nucleotides, using complementary base pairing, to the deoxyribose 3’ end of the new DNA strand which is forming
4 - DNA polymerase can only add DNA nucleotides in one direction, resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments.
5 - the fragments are joined together by ligase

Question 5

describe the process for the polymerase chain reaction

Answer 5

repeated cycles of heating and cooling amplify the target region of DNA

• DNA is heated to between 92 and 98 degrees to separate the strands
• it is then cooled to between 50 and 65 degrees to allow primers to bind to the target sequences
• it is then heated to between 70 and 80 for heat-tolerant DNA polymerase to replicate the region of DNA

Question 6

what is the process of speciation

Answer 6

isolation, mutation, selection

Question 7

describe the process of light absorption and photolysis

Answer 7

• energy absorbed by carotenoids is passed to chlorophyll
• absorbed light energy excites electrons in the pigment molecule
• transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase
• energy is used for photolysis, in which water is split into oxygen, which is evolved, and hydrogen ions, whcih are transferred to the coenzyme NADP

Question 8

describe the process of carbon fixation (the calvin cycle)

Answer 8

• ATP and hydrogen/NADPH from the first stage are used in carbon fixation/ the calvin cycle
• carbon dioxide is joined to ribulose biphosphate to form 3-phosphoglycerate
• this is controlled by the enzyme RuBisCO
• 3-phosphoglycerate is phosphorylated by ATP to form glyceraldehyde-3-phosphate (G3P)
• hydrogen/NADPH is required for this step
• G3P is used to make glucose and to regenerate ribulose biphosphate