(8) DNA & Protein Synthesis Flashcards
Compare structure of DNA in Eukaryotes and prokaryotes
Prokaryotic: Short, circular, with no free ends and not associated with histones. Prokaryotes do not have chromosomes as their DNA is not wrapped around histone proteins.
Eukaryotic:
Long, linear, with two ends and associated with histones, forming chromatin and then chromosomes.
Found inside the nucleus.
Describe two ways in which mitochondrial and chloroplast DNA differs from nuclear DNA in eukaryotic cells.
Mitochondrial & Chloroplast cells contain their own DNA. Hence more resembles prokaryotic DNA
Short and circular
Not associated with histones
Describe Transcription
DNA Unwinding:
DNA helicase breaks the hydrogen bonds between the two helixes of the DNA molecule, causing the double helix to unwind and exposing the nucleotide bases of the template strand.
Template Strand:
One of the DNA strands, known as the template strand, acts as a template for mRNA synthesis. The exposed bases on the template strand pair with free complementary RNA nucleotides (e.g., adenine with uracil, cytosine with guanine).
RNA Polymerase Action:
RNA polymerase catalyzes the formation of phosphodiester bonds between the RNA nucleotides, joining them together by a condensation reaction. This forms a strand of pre-mRNA.
Termination:
When RNA polymerase reaches a stop codon, transcription stops. The pre-mRNA is then released, and RNA polymerase detaches from the DNA.
mRNA Processing (Eukaryotes only):
In eukaryotes, the pre-mRNA undergoes splicing, where non-coding regions (introns) are removed and coding regions (exons) are joined together to form the mature mRNA.
Define degenerate code
A genetic code where multiple codons can code for the same amino acid.
Describe Translation:
After transcription, mRNA moves from the nucleus to the ribosome in the cytoplasm
The small subunit of the ribosome binds to the mRNA at the start codon.
A tRNA molecule with an anticodon complementary to the start codon (AUG) attaches to the mRNA. The tRNA is held in place by hydrogen bonds between the complementary base pairs on the mRNA and tRNA.
The second tRNA molecule with an anticodon complementary to the second mRNA codon binds to the mRNA.
A peptide bond is formed between the two amino acids carried by the tRNA. This process is catalysed by the enzyme peptidyl transferase, which is part of the ribosomal RNA (rRNA) in the ribosome.
The formation of the peptide bond requires ATP energy.
The ribosome moves along the mRNA to the next codon, and the first tRNA molecule is released from the ribosome.
