Unit 1: Human Cells: Chapter 3: Gene Expression

Question 1

Cell genotype

Answer 1

Genetic constitution of a cell. Determined by the sequence of DNA bases in the genes (genetic code).

Question 2

Phenotype

Answer 2

Sum total of physical and physiological characteristics. Determined by the proteins that are synthesized when the genes are expressed.

Final phenotype is result of information held in the genotype & environmental factors.

Genotype + Environment = Phenotype

Question 3

Nucleic acid

Answer 3

There are 2 types of nucleic acid

DNA - deoxyriboenucleic acid
RNA - ribonucleic acid

Question 4

RNA nucleotide

Answer 4

Each RNA nucleotide is made up of a

• a molecule of ribose sugar
• an organic base
• a phosphate group

Question 5

In RNA which base replaces thymine?

Answer 5

Uracil

Question 6

Name 3 ways in which DNA and RNA differ.

Answer 6

DNA is double stranded. RNA has only a single strand.
Complementary base partner of adenine is thymine in DNA uracil in RNA.
Sugar molecule in DNA is Deoxyribose; in RNA it is Ribose.

Question 7

Put the following in order of size from smallest to largest

• Protein
• Amino acid
• Enzyme
• Polypeptide chain

Answer 7

1. Amino acid
2. Polypeptide chain
3. Protein
4. Enzyme

Question 8

Describe the function of genetic instructions & how they work

Answer 8

Genetic instructions control an organism’s inherited characteristics. They are contained in the sequences of bases along the DNA strands in the cell nucleus. Characteristics are determined by biochemical processes controlled by enzymes. Enzymes are made of proteins whose exact molecular structure, shape & ability to perform its specific function all depend on the sequence of its amino acids. This critical order is determined by the order of bases in the organism’s DNA.
SO DNA controls the structure of enzymes & in so doing determines an organism’s inherited characteristics.

Question 9

What are the 4 bases in DNA?

Answer 9

Adenine
Cytosine
Guanine
Thymine

Question 10

How many types of amino acids are their in proteins?

Answer 10

20

Question 11

How may bases are there in any given group?

Answer 11

3.

Bases are grouped in triplets of one or more of 64 combinations.

Question 12

Ribosome

Answer 12

Roughly spherical structure within cytoplasm of cell where amino acids are assembled to synthesize proteins. Contain rRNA & enzymes essential for protein synthesis.

Question 13

mRNA

Answer 13

Messenger RNA (formed from appropriate section of DNA strand and carries information to ribosomes). As result of the base pairing rule, each mRNA molecule receives a nucleotide sequence complementary to the DNA template strand.

Question 14

tRNA

Answer 14

Transfer RNA (receives mRNA information at ribosome and translates the genetic information for protein synthesis within the ribosome. Composed of a single strand of nucleotides.

Question 15

Transcription

Answer 15

Synthesis of mRNA from a section of DNA. Transcription is initiated at a ‘promoter’ region of DNA strand.

Question 16

RNA polymerase

Answer 16

Enzyme responsible for catalyzing transcription. It moves along the DNA unwinding & opening up the strand by breaking the hydrogen bonds between the base pairs, to bring about synthesis of an mRNA molecule.

Question 17

Intron

Answer 17

Long section of DNA within a gene not involved in coding for polypeptide chain.

Question 18

Exon

Answer 18

Much smaller region of DNA strand within gene which codes for polypeptide.

Question 19

Primary mRNA transcript

Answer 19

First strand of mRNA molecule replicated from DNA template, containing both intron and exon sections.

Question 20

Mature mRNA transcript

Answer 20

mRNA strand that has had introns spliced out and remaining exons joined together to form a continuous sequence of nucleotides.

Question 21

Alternative segment RNA

Answer 21

Under certain circumstances, alternative segments of primary mRNA transcript can be treated as exons & introns. Same primary transcript has potential to produce several mature mRNA transcripts each with different sequence of base triplets & each coding for different polypeptide.
i.e. one gene can code for several different proteins & a limited number of genes can give rise to a wide variety of proteins.

Question 22

Splicing

Answer 22

Process by which intron sections of primary mRNA transcript are cut out & removed from molecule to leave just exon sections, which code for a polypeptide chain.

Question 23

Translation

Answer 23

Synthesis of protein as a polypeptide chain under direction of mRNA.

Question 24

Codon

Answer 24

Basic unit of genetic code. Base triplet in mRNA molecule carrying genetic message to ribosome. Each codon is complementary to a triplet of bases on original template DNA strand.

Question 25

Anticodon

Answer 25

Particular triplet of bases on tRNA molecule exposed complementary to an mRNA codon with a specific amino acid at tRNA attachment site.

Question 26

rRNA

Answer 26

ribsome Ribonucleic Acid

Question 27

Function of ribosome

Answer 27

To bring tRNA molecules bearing amino acids into contact with mRNA. Contains one binding site for mRNA and 3 binding sites for tRNA.

Question 28

tRNA binding sites - P, A & E

Answer 28

- site P holds the tRNA carrying the growing polypeptide chain. - site A holds the tRNA carrying the next amino acid to be joined to the growing chain by a peptide bond. - site E discharges a tRNA from the ribosome once its amino acid has become part of the polypeptide chain.

Question 29

Start codon

Answer 29

First base triplet in mRNA molecule which positions at P binding site in ribosome. Molecule of tRNA with its amino acid attaches at binding site P with hydrogen bonds between the mRNA start codon and the tRNA anticodon. Once 2 amino acids are adjacent they are joined by a peptide bond to the growing polypeptide chain.

Question 30

Peptide bond

Answer 30

Means by which amino acids are joined to form polypeptide chains.

Question 31

Stop codon

Answer 31

Region on mRNA strand which stops formation of polypeptide chain.

Question 32

Proteins

Answer 32

All proteins contain carbon, hydrogen, oxygen & nitrogen. Many also contain sulphur. Each protein is built up of a widely varying number of subunits called amino acids. Proteins are found in the membranes of all living cells & of cell organelles.

Question 33

Polypeptide

Answer 33

Chain of linked amino acids

Question 34

Enzymes

Answer 34

Each enzyme molecule is made of protein & folded in a way to expose an active surface to facilitate combining with a specific substrate.

Question 35

Intracellular enzymes (enzymes inside cells)

Answer 35

Speed up the rate of biochemical processes such as respiration & protein synthesis & therefore essential l for the maintenance of life.

Question 36

Hormones

Answer 36

Chemical messengers made of protein in blood to 'target' tissues where they exert a regulatory effect on growth and metabolism.

Question 37

Antibodies

Answer 37

Made of proteins & have a characteristic Y shape, produced by white blood cells to defend body against antigens.