Chapter 2 - Nucleic Acids And Proteins

Question 1

Organic molecules

1. 4 main elements found in organisms?
2. Organic compounds/molecules?
3. Inorganic compounds/molecules?
4. Main organic molecules?

Answer 1

1. Carbon, hydrogen, oxygen, nitrogen
2. Contain both carbon and hydrogen
3. Do not contain both carbon and hydrogen
4. Proteins, nucleic acids, polysaccharides (carbohydrates)

Question 2

Define

1. Monomer
2. Polymer
3. Condensation reaction
4. Nucleic acids
5. Deoxyribonucleic acid (DNA)
6. Ribonucleic acid (RNA)
7. Pyrimidines
8. Purines

Answer 2

1. Single unit (Sub-unit of an organic molecule)
2. When the sub-units are joined together to make a larger molecule
3. When two organic molecules are joined together, water is lost.
4. Composed of many nucleotide monomers that encode instructions for the synthesis of proteins in cells.
5. A double helix molecule containing the hereditary information transmitted through generations.
6. An unpaired chain of nucleotides with bases AUGC.
7. Single ringed bases - T, C, U
8. Double ringed bases - G, C

Question 3

Basic structure of DNA

• able to draw a diagram

Answer 3

• Phosphate
• Sugar (ribose)
• N-containing base: ATGC

Question 4

Three different forms of RNA

Answer 4

1. Messenger RNA (mRNA): carries a copy of the genetic instructions from the DNA to ribosomes in the cytoplasm.
2. Transfer RNA (tRNA): carries amino acids to the growing polypeptide chain during translation. One end of the tRNA carries the genetic code in a three-nucleotide sequence called the anticodon. The amino acid links to the 3’ end of the tRNA.
3. Ribosomal RNA (rRNA): makes ribosomes and assembles amino acids into s polypeptide chain.

Question 5

Define

1. Genetic code
2. Genes
3. Gene expression

• estimated number of human genes = 21,000

Answer 5

1. The set of rules by which the genetic information in DNA or mRNA is translated into proteins.
2. Sections of DNA that code for proteins.
3. The process by which the information in a gene is used to synthesise a protein. It involves transcription and translation.

Question 6

Genes

1. Coding region
2. Flanking region
3. Exons
4. Introns

Answer 6

1. The part of a gene that contains the coded information for making a protein.
2. The regions on either side of the coding region of a gene.
3. Coding regions of a gene, which are spliced together after introns are removed to form the mature mRNA before the gene can be translated into a protein.
4. Non-coding regions of a gene, which are removed.

Question 7

Process of protein synthesis

Answer 7

1. Transcription - process of copying the genetic instructions present in DNA to messenger RNA. Takes place in the nucleus.
   • RNA polymerase attaches to a specific promotor region in the upstream of a template strand.
   • DNA unzips and RNA polymerase reads the template strand.
   • RNA polymerase moves along the DNA template in a 3’ to 5’ direction and builds a complimentary pre-mRNA molecule using the code on the template strand.
   • DNA zips up again after it has been read.
   • RNA polymerase stops when it encounters a stop codon in the downstream region.
   • pre-mRNA is further modified before it leaves the nucleus through the nuclear pores.
   • introns are remover, exons are spliced together, a methylated cap added to 5’ end, and a poly-A tail is added to the 3’ end. diagram
   • the mRNA leaves the nucleus and moves to the cytosol where it becomes attached to ribosomes.
2. Translation - process of decoding the genetic instructions in mRNA into a protein built of amino acids (polypeptide chain). Takes place in the cytoplasm at free ribosomes or ribosomes on R.E.R.
   • the mRNA molecules attaches to a ribosome.
   • as the ribosome moves along the mRNA molecule, each codon pairs with the tRNA with the complimentary anti-codon in triplets.
   • the anticodon specifies which amino acids the tRNA carries. The amino acids are joined to form a polypeptide chain.
   • protein synthesis stops when a stop codon is reached. The ribosome subunits dissociate from the mRNA and the polypeptide is released.

Question 8

Define RNA polymerase

Answer 8

An enzyme that rewrites the DNA into a primary RNA script using a single template strand of DNA.

Question 9

Alternative splicing of pre-mRNA molecules from a single gene

Involves?

Answer 9

Exon juggling where different exons are combined to form several kinds of mRNA, each with a different base sequence.

Question 10

Structure of proteins

1. Amino acid structure?
2. R group does what?
3. How many amino acids, how many human cells can make, how many must be obtained from diet?
4. Amino acids joined together with, by process?

• amino acids are the monomers building blocks) of proteins.
• diagram

Answer 10

1. Amino group + a carboxyl group and a side chain (R group)
2. The R group varies in shape, polarity which gives each amino acid it’s unique biochemical properties. The R group determines how an amino acid will fold up into a functional protein and interact with other amino acids.
3. 20, human cells can make 11 of them, but 9 must be obtained from our diet.
4. Joined together with peptide bonds by the process of condensation.

Question 11

Define

1. Peptide
2. Polypeptide
3. Proteome

Answer 11

1. Two or more amino acids joined together by peptide bonds.
2. A chain of many amino acids.
3. Complete array of proteins produced by a single cell or organism in a particular environment.

Question 12

Once polypeptide released from the ribosome

Structures

1. Primary
2. Secondary
3. Tertiary
4. Quaternary

*italics a, special b

Answer 12

1. Primary structure (chain of amino acids): the sequence of amino acids in a polypeptide chain.
2. Secondary structure (a-helix or b-pleated sheet): polypeptide chain either coils to form an alpha helix or folds to form a beta-pleated sheet. Held by hydrogen bonds.
3. Tertiary structure (folding of the secondary structure): secondary structure folds further into a three-dimensional structure. Primarily due to side chain interactions.
4. Quaternary structure: a protein that is made up of more than one polypeptide chain.

Question 13

Gene expression

Define

1. Structural genes
2. Regulator genes

Answer 13

1. Genes that produce proteins that become part of the structure and functioning of an organism.
2. Genes that produce protest that control the activity of other genes - they control the expression of structural genes, whether they are switched on or off.

Question 14

Gene structure

1. In prokaryotes
2. In eukaryotes

Answer 14

1. Several structural genes with related functions are groups together between UTRs. Grouping of their structural genes and regulatory elements are called operons.
2. Only one structural gene is enclosed by UTRs.

Question 15

How do genes switch on and off?

Answer 15

Regulator genes produce proteins called:
• DNA-bonding proteins - bind near the genes and directly switch genes on or off.
• signalling proteins - bind to receptors on the surface of a cell and trigger signals inside the cell that switch genes on or off.

Question 16

Define homeotic genes

Answer 16

Genes that control embryonic development.

Question 17

Gene regulation in prokaryotes- the lac operon

1. Promoter
2. Operator
3. Lac I gene
4. When lactose is absent
5. When lactose is present
   * diagrams

Answer 17

1. Where RNA polymerase binds, then starts transcription of the three downstream lac genes.
2. Provides a binding site for a repressor.
3. A regulator gene that encodes a repressor protein.
4. Repressor protein is active and binds to the operator, physically blocking RNA polymerase from attaching to the promotor. So, the lac operon cannot be transcribed.
5. A lactose molecule binds to the repressor protein, changing its shape and inactivating it so that it cannot bind to the operator. RNA polymerase can now attach to the promotor and start transcription of the structural genes.

Question 18

DNA replication

1. DNA is semi-conservative meaning
2. Process

*just before division, the DNA replicates.

Answer 18

1. Each daughter DNA molecule ends up with one old strand and one new strand.
2. Process:
   • two strands of DNA are separated by an enzyme called DNA helicase which requires ATP, other proteins keep the strands apart.
   • a primer (short strand of DNA) is added to the single-stranded DNA template.
   • the enzyme DNA polymerase then adds the correct nucleotides in the direction 3’ to 5’.
   • primer later removed by editing enzymes.

Question 19

Define Okazaki fragments

Answer 19

Short DNA fragments synthesised discontinuously then later linked together to create the lagging strand during DNA replication.