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 from transcription binds to ribosome in cytoplasm
2. 2 codons can fit inside ribosome at a time- one tRNA molecule bind to first codon; has anticodon complementary to it (allows correct ones to bind)
3. Each tRNA carries specific amino acid (bound to tRNA using ATP) into ribosome
4. tRNA binds to 2nd codon in ribosome. As tRNA binds to mRNA, corresponding amino acid bought into ribosome. The 2 amino acids in ribosome form a peptide bond
5. As 2 amino acids bind, ribosome moves along mRNA strand, so a new codon enters ribosome. Complementary tRNA binds to new codon, new amino acid brought in; peptide bond formed with this and existing amino acid chain (polypeptide)
6. Ribosome reaches STOP codon, no corresponding tRNA molecule. Polypeptide chain released from ribosome; is now formed, can complete its function