Chapter 8 - DNA, genes and protein synthesis

Question 1

what is a gene?

Answer 1

base sequence of DNA that codes for the amino acid sequence of a polypeptide or RNA

Question 2

how did scientists discover that 3 bases code for each amino acid?

Answer 2

4 bases x 3 = 64

20 amino acids - degenerate code

Question 3

state 5 features of the genetic code

Answer 3

• degenerate code
• triplet always read in a particular direction
• start codon always same triplet
• 3 triplets do not code for any amino acid - stop codons
• non-overlapping code
• universal code

Question 4

state the structures in a chromosome from smallest to largest (6)

Answer 4

• base pairs
• double helix
• DNA histone complexes
• DNA histone complex coiled
• coils fold to form loops
• loops coil and pack together to form chromosomes

Question 5

what are homologous pairs

Answer 5

• one provided from mother one from father

Question 6

what is the diploid number

Answer 6

total number of homologous pairs

Question 7

what is an allele

Answer 7

different forms of a gene

Question 8

what is mRNA

Answer 8

long, single stranded base sequence in single helix small enough to leave nucleus through pores

Question 9

what is tRNA

Answer 9

small, single stranded molecule of bases in clover leaf structure, with attachment site for specific amino acid and 3 bases opposite forming an anticodon

Question 10

what is a genome

Answer 10

the complete set of genes in a cell

Question 11

what is a proteome

Answer 11

the full range of proteins produced by the genome

Question 12

define transcription

Answer 12

the process of making pre-mRNA using part of the DNA as a template

Question 13

outline the process of transcription

Answer 13

• DNA helicase separates strands of DNA at specific region
• template strand pairs with complimentary nucleotides present in the nucleus
• RNA polymerase moves along to join nucleotides for form pre-mRNA molecule
• uracil instead of thymine
• DNA strands rejoin behind the forming molecule
• when RNA polymerase reaches the stop codon the molecule pre-mRNA is complete and is released

Question 14

what is splicing

Answer 14

the removal of introns from pre-mRNA to form mRNA

Question 15

how are polypeptides synthesised (6)

Answer 15

• ribosome becomes attached to starting codon
• tRNA with complimentary aniticodon pairs with codon on mRNA, carrying specific amino acid
• tRNA molecules pair with complimentary codons on mRNA all along the molecule
• ribosome moves along mRNA binding together tRNA molecules in a strand along with the amino acids
• as this happens, the previous tRNA are released from the amino acid leaving behind a strand of amino acids
• when ribosome reaches a stop codon it stops addition of bases and releases the amino acids