Chapter 8: DNA, Genes and Protein Synthesis

Question 1

What is a gene?

Answer 1

A section of DNA that contains the coded information for making polypeptides and functional RNA.

Question 2

In what form is the coded information?

Answer 2

A specific sequence of bases along the DNA molecule.

Question 3

What is a locus?

Answer 3

The particular position on a DNA molecule where the gene is located.

Question 4

What does a gene code for?

Answer 4

• The amino acid sequence of a polypeptide.

- Or a functional RNA, including ribosomal RNA and transfer RNAs.

Question 5

Why is the genetic code considered degenerate?

Answer 5

Most amino acids are coded for by more than one triplet.

Question 6

Why is the genetic code considered non-overlapping?

Answer 6

Each base is read only once.

Question 7

Why is the genetic code considered universal?

Answer 7

With a few minor exceptions, each triplet codes for the same amino acid in all organisms. (indirect evidence for evolution)

Question 8

What are exons?

Answer 8

Coding sequences- required (EXit the nucleus)

Question 9

What are introns?

Answer 9

Non-coding sequences- removed (stay IN the nucleus)

Question 10

What is a chromosome?

Answer 10

A thread-like structure in which DNA is tightly packaged within the nucleus.

Question 11

What is a centromere?

Answer 11

A specialised DNA sequence of a chromosome that links a pair of sister chromatids.

Question 12

What is a chromatid?

Answer 12

One thread of a chromosome.

Question 13

How is DNA packed into a chromosome?

Answer 13

1: DNA molecule is combined with histones.
2: DNA-histone complex is coiled.
3: Coils fold to form loops.
4: Loops coil and pack together to form the chromosome.

Question 14

What is a cell that has paired chromosomes (one from each parent) called?

Answer 14

Diploid

Question 15

What are two chromosomes that carry the same genes called?

Answer 15

Homologous pairs

Question 16

Which type of cell division produces four daughter cells, each with half the number of chromosomes as the parent cell?

Answer 16

Meiosis

Question 17

What is one type of alternative form of a gene called?

Answer 17

Allele

Question 18

What ‘change’ in the base sequence of a gene produces new allele of that gene?

Answer 18

Mutation

Question 19

What is an enzyme with a new shape that may not fit its substrate called?

Answer 19

Non-functional enzyme

Question 20

What is a codon?

Answer 20

The sequence of three bases on mRNA that codes for a single amino acid.

Question 21

What is a genome?

Answer 21

The complete set of genetic material in an organism.

Question 22

What is a proteome?

Answer 22

The full range of proteins produced by the genome.

Question 23

What is RNA?

Answer 23

Ribonucleic acid
A polymer made up of repeating mononucleotide sun-units. It forms a single strand of: the pentose sugar ribose, one of the organic bases adenine, guanine, cytosine and uracil, and a phosphate group.

Question 24

What type of strand is a DNA, mRNA and tRNA molecule?

Answer 24

DNA: double
mRNA: single
tRNA: single

Question 25

What is the order of increasing size of DNA, mRNA and tRNA?

Answer 25

tRNA- smaller
mRNA: variable
DNA: largest

Question 26

What type of shape is a DNA, mRNA and tRNA molecule?

Answer 26

DNA: double helix
mRNA: single helix
tRNA: clover shape

Question 27

What type of sugar is present in a DNA, mRNA and tRNA molecule?

Answer 27

DNA: deoxyribose
mRNA: ribose
tRNA: ribose

Question 28

What are the different bases in a DNA, mRNA and tRNA molecule?

Answer 28

DNA: A, T, C, G
mRNA: A, U, C, G
tRNA: A, U, C, G

Question 29

What is the quantity of DNA, mRNA and tRNA molecules in cells?

Answer 29

DNA: constant (gametes)
mRNA: varies
tRNA: varies

Question 30

What is the stability of DNA, mRNA and tRNA molecules like?

Answer 30

DNA: very stable
mRNA: unstable
tRNA: more stable than mRNA but less stable than DNA.

Question 31

What is an anticodon?

Answer 31

Three bases at the opposite end of the tRNA.

Question 32

What does the anticodon pair with?

Answer 32

The complementary codon on the mRNA.

Question 33

What are the stages of protein synthesis?

Answer 33

1: Transcription of the gene in the nucleus- an mRNA strand is formed.
2: Processing of the mRNA
3: Translation of the mRNA in a ribosome- a polypeptide chain is formed.
4: Modification of the protein

Question 34

What is the process of transcription?

Answer 34

(condensation reaction)

1: DNA helicase unwinds the double helix of DNA by breaking the hydrogen bonds between the base pairs.
2: The two strands of DNA are separated so free RNA nucleotides can fit in.
3: Free RNA nucleotide bases bind to the template DNA by their complementary base pair rules.
4: RNA polymerase joins the ribose phosphate backbone of the RNA nucleotides to form a molecule of pre-mRNA.
5: The single pre-mRNA strand moves away from the DNA helix and RNA polymerase zips the two strands of DNA back together.
6: The pre-mRNA strand is processed through splicing to form mRNA that is ready for translation.

Question 35

What is splicing?

Answer 35

The base sequences corresponding to the introns are removed and the functional exons are joined together.

Question 36

What is the process of translation?

Answer 36

1: A ribosome attaches to the mRNA at an initiation codon.
2: The bond between the amino acid and the tRNA is cut and a peptide bond is formed between the two amino acids. This operation is catalysed by ribozyme.
3: The polypeptide chain elongates one amino acid at a time, and peels away from the ribosome, folding up into a protein as it goes. This continues for hundreds of amino acids until a stop codon is reached, when the ribosome falls apart, releasing the finished protein.
4: The next amino acid-tRNA attaches to the adjacent mRNA codon. The anticodon on the tRNA binds to the codon on the mRNA.
5: The ribosome moves along one codon so that a new amino acid-tRNA can attach. The free tRNA molecule leaves to collect another amino acid. The cycle repeats from step 3.