Gene expression

Question 1

Summary of what happens

Answer 1

Gene segments of DNA, are
- Transcribed into molecules of mRNA (TRANSCRIPTION)
- Then they are translated into amino acid sequences that make proteins

Question 2

main steps

Answer 2

• Transcription (DNA to mRNA)
• RNA Processing
• Translation (mRNA to protein)

Question 3

Gene structure

Answer 3

3’ - upsteam - non-coding DNA
Promotor region - marks the start of a gene
Template stand (Antisense)
Terminator region - marks the end of a gene

Question 4

Transcription steps

Answer 4

• Enymze RNA polymerase attaches to a specific promoter sequence of DNA (upstream) in the template strand. The DNA unzips and template bases are exposed.
• The DNA template is used to build an mRNA molecule. RNA polymerase moves along the stand in 3’ to 5’ direction, which creates a complementary strand of mRNA (pre-messenger RNA)

Question 5

RNA processing

Answer 5

happens to eukaryotes only, transcription produces pre-mRNA molecules. These molecules are modified to form ( mature mRNA) via
- SPLICING: removal of introns and remaining exons are spliced together

• Adding a 5’ methyl cap: (the 5’ end of pre-mRNA is capped with a guanine methylbase. Prevents enzyme attacks and contributes to its stability)
• Adding a 3’ poly - A - trail: (the 3’ end has a poly adenine (A) tail on the pre-mRNA contributes to stability)

the 3’poly-A-tail and 5’methyl cap structures prevent degradation

Question 6

Introns and Exons

Answer 6

Eukaryotic genes contain segments of protein-coding sequences (Exons) that are interrupted by non-protein coding sequences (INTRONS)

Question 7

Translation

Answer 7

Occurs in the cytoplasm
- Translation is the process of building a polypeptide chain from amino acids, guided by the sequence of nitrogenous bases on the mRNA

Question 8

Translation involves

Answer 8

-mRNA: carries the genetic code to the translated from the DNA to the ribosome

• Amino acids: monomers of the polypeptides

-Transfer RNA: molecules (tRNA) transport amino acids to the ribosome

• Ribosomes - provide the environment for mRNA/tRNA attachment and amino acid binding

Question 9

Translation process

Answer 9

• mRNA strand (carrying a transcribed copy of the gene) binds with a ribosome

-tRNA carries a specific amino acid to the ribosome

-anticodons of the tRNA binds with a complementary codon on the mRNA

• Specific amino acid, carried by the tRNA, is added to the growing polypeptide, via a peptide bond