DNA, Genes & Protein Synthesis

Question 1

What are DNA molecules like in prokaryotic cells?

Answer 1

Short, circular and not associated with proteins

Question 2

What are DNA molecules like in eukaryotic cells?

Answer 2

Very long, linear and associated with proteins

Question 3

Locus def

Answer 3

The fixed position of a gene

Question 4

Introns def

Answer 4

Non-coding regions of nucleotide sequence (removed from pre-mRNA)

Question 5

Exons def

Answer 5

Coding regions of nucleotide sequence (remain present after introns have been removed)

Question 6

What are genes like in eukaryotic cells (introns and exons)

Answer 6

Discontinuous, has both introns and exons in pre-mRNA, introns are cut out by endonucleases, exons are spliced together with ligases

Question 7

What are genes like in prokaryotic cells (introns and exons)

Answer 7

Continuous, lacks introns

Question 8

Genome def

Answer 8

The complete set of genes in a cell

Question 9

Non-overlapping def

Answer 9

Triplets are read exclusively and no two amino acids have the same code

Question 10

Gene def

Answer 10

A length of DNA on a chromosome that codes for a sequence of amino acids in a particular polypeptide

Question 11

Degenerate def

Answer 11

An amino acid is encoded by more than one codon

Question 12

How many different amino acids are there in proteins?

Answer 12

20

Question 13

Proteome def

Answer 13

The full range of proteins a cell is able to make

Question 14

How is a protein assembled after translation?

Answer 14

Sequence of amino acids in the polypeptide is determined. Genes can precisely know which proteins a cell manufactures. Control the activities of the cell. Sometimes a single polypeptide chain is enough to be functional. Mostly many polypeptides are linked together for it to be functional (quaternary)

Question 15

How are proteins made (in terms of structures)?

Answer 15

Polypeptide is coiled or folded (secondary), secondary structure is folded (tertiary), many polypeptide chains with any non-protein group link together (quaternary)

Question 16

Describe transcription

Answer 16

DNA unzips as DNA helicase acts on cistron to break hydrogen bonds between bases. RNA polymerase catalyses addition of free nucleotides complementary to the template strand to form mRNA. RNA polymerase separates when it reaches the stop codon

Question 17

How are proteins universal?

Answer 17

The same three bases code for the same amino acid

Question 18

What is a homologous pair of chromosomes?

Answer 18

Two chromosomes that code for the same genes in a cell.

Question 19

How does the arrangement of prokaryotic DNA differ from the arrangement of human DNA?

Answer 19

Prokaryotic DNA is circular whereas human DNA is linear. Prokaryotic DNA is not associated with proteins or histones. Prokaryotic DNA is only one molecule/one piece of DNA.

Question 20

What is the effect of a mutation of a gene on the protein produced?

Answer 20

A base will change in the DNA sequence changing the base sequence of the mRNA strand. This means that incorrect amino acids with different primary structures will be formed resulting in a different tertiary structure and a different shape of the active site.

Question 21

How does a nucleotide base sequence synthesise a polypeptide?

Answer 21

Transcription happens in the nucleus. DNA helix case unzips the double stranded molecule. RNA polymerase catalyses the addition of free nucleotides which complement the template DNA strand to form a strand of mRNA. The polymerase unattaches once it reaches the stop signal. Next translation help happens once the mRNA strand leaves the nucleus through a nuclear pore and attaches to a ribosome. Bases are read six at a time (wto triplets). These codons have complementary anticodons on tRNA strands which are attached to a single amino acid. As the mRNA strand is read complementary tRNA attaches to the codons. The amino acids form peptide bonds between themselves and the tRNA strand is free to leave and collect another amino acid from the amino pool. The bases from the mRNA are broken from the strand and become free nucleotides. Once a stop codon is reached the ribosome no longer reads the strand and a polypeptide chain is formed

Question 22

Why do single base deletion mutations on an exon produce an non-functional protein?

Answer 22

Deletion removes one base from the sequence which causes a frame-shift. This is when all bases, after the base removed, move up the sequence resulting in different codons, meaning different amino acids will be formed. This changes the polypeptide chain by affecting hydrogen, ionic and sulfur bonds so the protein will be non-functional.

Question 23

What is the effect of single base substitution on introns?

Answer 23

Introns are non-coding and will be removed from pre-mRNA. Therefore it is not translated and has no effect on the protein produced. Moreover, substitutions do not cause a frame shift so the rest of the sequence will be unchanged.

Question 24

Which part of the cell cycle is most likely to have gene mutations occur? Why?

Answer 24

Interphase because it’s the longest phase

Question 25

How is the chromosome number half during meiosis?

Answer 25

The chromosomes are put into homologous pairs and one of each goes into each daughter cell.

Question 26

How does crossing over increase genetic diversity?

Answer 26

Homologous pairs for my bivalent. A chiasma form which entangle together. Equal lengths of nonsister chromatids are exchanged. New combination of alleles is formed.