Biology - Chapter 8: DNA, Genes and Protein Synthesis

Define gene. (1)

• Sequence of DNA bases that codes for a polynucleotide or functional RNA

Define what it means for the genetic code to be Universal. (1)

• The same triplet/ codon always codes for the same amino acid

Define what it means for the genetic code to be degenerate. (1)

• More than one triplet/codon codes for the same amino acid

Define what it means for the genetic code to be non-overlapping. (1)

• Each base is only part of one triplet/codon

Define chromosomal mutation. (1)

Change in the number of chromosomes

Define allele. (1)

Different forms of a gene

Define locus. (1)

Fixed position of a gene in a chromosome

Define homologous pair of

chromosomes. (1)

• A pair of chromosomes that contains the same genes

Compare chromosome in Eukaryotc and prokaryotic cell. (5)

Eukaryotic DNA: Introns, Longer,

Associated w/histones, Linear, No plasmids

Prokaryotic DNA: No Introns, Shorter, not associated w/histones, Circular, Plasmids

Describe and explain the appearance of the chromosome in the diagram. (2)

• After DNA replicates / interphase / S-phase in eukaryotic cells
• (each chromosome) made of two chromatids joined together by centromere

Define genome. (1)

• Range of different genes in a cell

Define proteome. (1)

Range of different proteins that a cell is able to make / DNA is able to code for

Define triplet. (1)

Sequence of three DNA bases that codes for a specific amino acid

Define codon. (1)

Sequence of three mRNA bases that codes for a specific amino acid

Define anticodon. (1)

Sequence of three tRNA bases that codes for one specific amino acid

Compare and contrast the structure of mRNA and tRNA. (4)

mRNA: longer, no amino acid binding site, linear, no hydrogen bonds, has codons
tRNA: shorter,has animo acid binding site, clove shaped, hydrigen bonds , has anticodons
Both: Single chain, nucleotides same composition, joined phosphodiester bonds in condensation reaction

What molecule us produced in transcription? (1)

• mRNA / messenger RNA

Where in the cell does transcription take place? (1)

• In the nucleus

How is transcription different in eukaryotic and prokaryotic cells? (3)

In Eukaryots only
• pre-mRNA is formed
• pre-mRNA contain introns
• Introns are spliced/removed to make mRNA

Describe transcription in eukaryotic cells. (6)

• H-bonds between complementary bases in DNA molecule are broken
• One strand of DNA acts as template strand
• Free RNA nucleotides attach to complementary base in DNA template strand
• Adenine in DNA complementary to Uracyl in RNA; Thymine in DNA complementary to Adenine in RNA; Guanine and cytosine complementary to each other
• RNA polymerase joins adjacent nucleotides in phosphodiester bonds
• Via condensation reaction / using ATP
• Pre-mRNA is formed and spliced forming mRNA / introns removed from pre-mRNA to form mRNA
• mRNA leaves nucleus through nuclear pore

What is splicing? (2)

• Remove introns / non-coding regions/codons
• From pre-mRNA to make mRNA in eukaryotic cells

What molecule is produced in translation? (1)

• Polypeptide chain

Where does transcription take place? (1)

• In ribosomes in the cytoplasm
• In ribosomes in the rough endoplasmic reticulum

Describe the importance of ATP in translation. (3)

• Releases energy for
• Amino acids to be joined together in peptide bonds via condensation reactions/ by ribosome
• Specific amino acid to be attached to tRNA

Describe how mRNA is translated. (6)

• mRNA leaves nucleus through nuclear pore and attaches to ribosomes in the cytoplasm / endoplasmic reticulum
• Anticodon in tRNA binds to complementary codon in mRNA
• On specific tRNA brings one specific amino acid
• Ribosome joins amino acids in peptide bond
• Using ATP in condensation reactions
• tRNA detaches
• Ribsome moves along mRNA until STOP codon forming polypeptide