Unit 9: Molecular Genetics

Question 1

What is DNA

Answer 1

**Genetic material **of all living organisms

Hereditary information is passed to offspring using DNA.

*Some viruses use RNA but are not considered living.

Question 2

What are the components of a nucleotide?
Draw and label

Answer 2

Phosphates, pentose sugars, and bases.

Question 3

What is a covalent bond?

Answer 3

It is sugar-phosphate bonding between nucleotides.

Between the phosphate of one nucleotide and the sugar of another

Forms a strong sugar/phosphate backbone

Covalent bonds can be specified phosphodiester bonds

Question 4

What are the nitrogenous bases? Types

Answer 4

Bases in each **nucleic acid **that forms the basis of a code

Adenine, Guanine, Cytosine, Thymine,

In RNA Uracil instead of Thymine

Bases can be classified as Purine (A, G) or Pyrimidine (C, T, U).

Question 5

Talk about RNA as a** polymer** formed by condensation of **nucleotide monomers
**

Answer 5

A polymer formed by condensation of nucleotide monomers.

RNA is a **single strand **of nucleotides whereas DNA is double stranded

Condensation reactions: removal of water to create bond → this will create covalent bonds between nucleotides in the RNA

Question 6

What is the structure of DNA?
Draw and label

Answer 6

Double helix made of two antiparallel strands of nucleotides

Two strands are linked by hydrogen bonds between complementary base pairs

*A-T
**G-C **

Question 7

What are the main differences between DNA and RNA?

Answer 7

Similarities:
* Both polymer of nucleotides (phosphate, a sugar, nitrogenous base)
* Cytosine pairs with Guanine

Differences:
DNA
* Double-stranded
* Has deoxyribose sugar
* Uses thymine.

**RNA **
* Single-stranded
* Has ribose sugar
* Uses uracil.

Question 8

What is the role of complementary base pairing?

Answer 8

It allows genetic information to be replicated accurately during DNA replication.

Follows the rules of complementary base pairing

Question 9

What does the term ‘semiconservative’ mean ?

Answer 9

Each resulting DNA molecule consists of **one original (parent) strand ** and one new strand during DNA replication

Each parent strand is used as a template for synthesizing a new strand

Question 10

Diversity of possible DNA base sequences and the limitless capacity of DNA for storing information

Answer 10

DNA molecules can vary in length
Many possibilities for unique sequences (4 bases)
DNA is only 2 nm in diameter, so cells can store long lengths of DNA
Even the tiniest organisms can hold billions of base pairs

Question 11

Conservation of the genetic code across all life forms as evidence of universal common ancestry

Answer 11

The same codons on RNA code for the same amino acids in almost every organism
Universal genetic code → it is interpreted the same way
Evidence that all life arose from a common ancestor

Question 12

What is DNA replication? What is its role?

Answer 12

DNA replication: production of an exact copy of a DNA strand

**Reproduction: **passing hereditary information to offspring

**Growth & repair: **process of cell division to create new cells (requires replication of DNA)

Question 13

Semi-conservative nature of DNA replication and role of complementary base pairing? Why are they important

Answer 13

Semi-conservative replication: DNA replication in which each DNA molecule consists of one original strand and one new strand

Relies on complementary base pairing..the parent strand is used as a template to determine the order of bases in the new strand

These two allow for high accuracy in replication

Question 14

What is the role of helicase?

Answer 14

During DNA Replication,
Unwinds and breaks hydrogen bonds between DNA strands.

Question 15

What is DNA polymerase ?Its function?

Answer 15

It is en enzyme.
During DNA replication, it adds free nucleotides to the new strand, creating bonds between nucleotides.

Question 16

What is polymerase chain reaction (PCR)?

Answer 16

A method to amplify DNA by making many copies of a DNA segment.

Uses primers and Taq polymerase, involves temperature changes.

• Primer (short segment of DNA) is added to signal where to start copying
• Taq polymerase is a heat-tolerant DNA polymerase that is also added, along with free nucleotides
• Heating it up (breaking hydrogen bonds) and cooling (for binding) allows for fast replication

Question 17

What is gel electrophoresis used for? Explain its logic

Answer 17

Gel electrophoresis separates DNA molecules by length

1. Put DNA fragments into one end of porous gel
2. Apply electricity (negative electrode at DNA end)
3. DNA is also negative, so the repelling force moves DNA through the gel

Shorter fragments go further

• Paternity Testing
• Testing for coronovirus

Explanation:
To create a DNA profile, a DNA sample is obtained from the child, alleged biological father and mother, and analysed.

Sequences that vary a lot between individuals such as VNTRs are selected and amplified using PCR

The DNA is then split into fragments and the fragments are separated by size and charge, using gel electrophoresis

Question 18

What is transcription?
What is the role of RNA polymerase?

Answer 18

Transcription: using a strand of DNA as a template to synthesize a strand of DNA to make RNA

RNA polymerase: enzyme that separates the strands, adds RNA nucleotides and creates the sugar-phosphate bonds to create a continuous strand

Follows the complementary base pairing rules. But RNA has uracil instead of thymine

Question 19

What is the role of RNA polymerase in transcription?

Answer 19

Enzyme that
- Separates the strands
- Adds RNA nucleotides
- Creates the sugar-phosphate bonds to create a continuous strand

Question 20

What is the difference between sense and antisense strands of DNA?

Answer 20

One of the parent strands of DNA will be used as a template to synthesize the RNA

Sense strand: contains the genetic information to be copied

Antisense strand: the strand that is actually used for transcription

Complementary base pairing rules ensure that the RNA produced is an exact copy of the gene

**A T G C C A T **→ sense strand

A U G C C A U → mRNA (identical to the DNA in the sense strand)
**T A C G G T A **→ antisense strand is used as a template

Question 21

Explain the stability of DNA templates? Why is it beneficial?

Answer 21

DNA is most stable when two strand are together

This stability prevents changes in bases

When the strands are temporarily separated, mutations can occur
(during transcription)

In somatic cells that do not divide, such sequences must be conserved throughout the life of a cell

Question 22

Explain the link between transcription and gene expression

Answer 22

Gene expression: protein production using the sequence of bases in a gene

Not all genes are expressed.

Only the genes that need to be expressed will be transcribed

For gene expression : turns on all the genes needed → transcription → translation → protein synthesis

Question 23

What is translation?

Answer 23

The synthesis of polypeptides from mRNA.

Message is being carried to the cytoplasm on a ribosome where that polypeptide will be produced (amino acid chains)

Question 24

What is the role of mRNA and tRNA in translation?

Answer 24

mRNA = messenger RNA, has codons (groups of 3 bases)

tRNA transfers amino acids to the ribosome and has an anticodon complementary to the mRNA codon.

Ribosome has two subunits:
- Small subunit binds to mRNA
- Large subunit has tRNA binding sites and also a catalytic site to create peptide bonds

Question 25

What defines a codon in mRNA and anticodon in tRNA

Answer 25

Codon: A group of three bases on mRNA. Anticodon: group of 3 bases on tRNA that is **complementary to a specific mRNA codon**.

Question 26

Outline the process of translation

Answer 26

Process of translation: 1. **mRNA** attaches to the subunit of the ribosome 2. **tRNA** with an anticodon complementary to the start codon attaches 3. The ribosome slides to the next codon and the next tRNA attaches 4. Amino acids are joined together (peptide bonds) 5. Continues until a stop codon is reached 6. Polypeptide chain will detach

Question 27

Features of genetic code? (Universal, degenerate) Explain. What is the advantage of degeneracy?

Answer 27

- Code is read in triplets, which allows for 64 combinations of the 4 bases - **Universal:** the same codons make the same acids in all organisms and viruses - **Degenerate:** different codons can code for the same amino acid → Advantage: this allows that mutates codons still coding for the same amino acid

Question 28

DNA G G T A C A C A T What is mRNA and tRNA?

Answer 28

mRNA C C A U G U G U A tRNA G G U A C A C A U

Question 29

What are mutations? Types of mutations? What could be the results?

Answer 29

Mutation: change to the base sequence of a gene, they are **random** Might change **protein structure and function.** Three types 1. Base substitution (different nucleotide) - Might be **silent** due to **degeneracy**, it will still code for the same amino acid - **Conservative:** Might change into a **similar** amino acid so functions nearly normal - **Non-conservative:** Might change into a very different amino acid, structure and function changes - **Non-sense:** When the mutation causes a stop codon to replace an amino acid the polypeptide chain will be shorter. **Substitution does not change the reading frame. ** Example: **haemoglobin mutation resulting in sickle cell anemia** **Protein shape and function might change** 2. Insertion (adding an extra nucleotide) 3. Deletion (removing a nucleotide) Inserting and deleting a base **changes the reading frame of a codon.** Therefore all the codons will change and the polypeptide chain will be completely **different.**

Question 30

What is a single-nucleotide polymorphism (SNP)?

Answer 30

A base substitution mutation that may or may not change an amino acid in a polypeptide. An SNP (single-nucleotide polymorphism) is created when one nucleotide is replaced by another (e.g., A→T) during DNA replication or repair. (Substitution)

Question 31

What causes gene mutations?

Answer 31

Mutagens - Causes **chemical changes **to DNA - E.g. radiations (UV, X-rays etc.) - E.g. Chemical substance (tobacco smoke) Errors in DNA replication or repair - They are** random** - Mutations can occur **anywhere **in the genome - Most mutations acquired during an organism’s lifetime are **not passed to offspring, if they are not in gamete cells**

Question 32

Somatic cells and germ cells? Consequences of mutation in germ cells and somatic cells

Answer 32

Somatic cells : **body cell** **Not passed **to offspring Example: oncogene mutations that cause cancer Germ cell: **gamete-producing cell** **Can be passed** to offspring Most are harmful Important to minimise exposure They are not passed to offspring unless they occur in gamete cells

Question 33

What is the original source of all genetic variation?

Answer 33

Gene mutation Because they create **new alleles (new versions of genes)** Most mutations are either silent or harmful Rare, beneficial mutations have an **advantage for (natural selection)** Environments change → species must change → this is driven by mutations to survive that change

Question 33

What is an allele?

Answer 33

Different versions of a gene

Question 33

How do new alleles arise?

Answer 33

From mutations, increasing genetic variation