4 Genetic Information & variation- DNA & protein synthesis

Question 1

What is the genome?

Answer 1

Complete set of genes in an individual’s DNA
Genes in genome encode the different proteins a cell needs

Question 2

What is the proteome?

Answer 2

Full range of proteins an individual can produce

Question 3

What is mRNA?

Answer 3

-Transcribed from DNA in nucleus to produce single-stranded RNA
-mRNA strand= complementary to DNA base sequence
-Travels from nucleus to ribosomes in cytoplasm (translate mRNA into amino acids, synthesise polypeptide)

Question 4

What is the structure of mRNA?

Answer 4

-Longer chain than tRNA
-Single stranded helix molecule
-Chemically unstable; (only present for protein synthesis)

Question 5

What is tRNA?

Answer 5

-Vital for translation
-Reads mRNA codons, brings corresponding amino acid into ribosome; important so that protein is assembled correctly

Question 6

What is the structure of tRNA?

Answer 6

-Clover-like shape
-Each molecule has anticodon, binding site complementary to a specific codon on mRNA
-Amino acid corresponding to specific anticodon binds to specific attachment (on stalk) site on tRNA
-Short chain
-Chemically stable

Question 7

What are the steps involved in transcription?

Answer 7

1. RNA polymerase binds to locus of gene to be transcribed
2. As it binds to DNA, hydrogen bonds between the strands break, strands separate. Bases of target gene exposed
3. RNA polymerase binds free-floating RNA nucleotides to template strand (DNA strand complementary to base sequence of target gene). RNA nucleotides form strand of mRNA complementary to template strand.
4. Phosphodiester bonds form between nucleotides in condensation reaction, forms completed mRNA strand (pre-mRNA in eukaryotes)
5. RNA polymerase reaches STOP codon, stops separating DNA and making mRNA
6. RNA polymerase separates mRNA strand from template strand. (spliced in eukaryotes) Hydrogen bonds between the 2 DNA strands form again, rejoin together
7. mRNA strand leaves nucleus, enters cytoplasm. Used in translation

Question 8

What is the difference between transcription in eukaryotes and prokaryotes?

Answer 8

Prokaryotes- transcription results directly in production of mRNA from DNA
Eukaryotes- transcription results in pre-mRNA, which is spliced to form mRNA (introns removed, exons joined together)

Question 9

What are the steps involved in translation?

Answer 9

1. mRNA molecule attaches to a ribosome in cytoplasm after leaving the nucleus
2. Free molecules of tRNA in cytoplasm bind with their specific amino acid on their binding centre, bring them to the mRNA
3. The anticodon on each tRNA binds w/ a complementary codon on mRNA
4. Two tRNAs fit into the ribosome at a time, both bring their amino acid. The two amino acids make a peptide bond (use energy from ATP)
5. Process continues; ribosome moves along mRNA, reading next codon until a ‘stop’ codon is reached on mRNA; translation stops & amino acid chain is complete + forms final polypeptide