DNA Structure and Replication: Unit 4, Topic 1

Question 1

What is DNA (Deoxyribonucleic Acid) What is genes?

Answer 1

DNA
- Organisms genetic material
- contains instructions for the cell to produce proteins
- spiralling chain like molecule made of nucleotides. (A, C, G, T)

Genes
- single section of DNA that contain genetic information

Question 2

Explain DNA in Eukaryotes (the nucleus)

Answer 2

• found in the nucleus, chloroplasts (in plants) and mitochondria.

DNA in the nucleus:
- organised in strands
- exists in a double helix structure

Histone: a protein that helps condense DNA in the nucleus into chromatin (allows it to fit into the nucleus)

When cells prepare to divide, the chromatin condenses by coiling up to form chromosomes.

Chromosome = an entire chain of DNA along with a group of stabilising proteins

unduplicated/single chromosome - single, long DNA double helix molecule coiled around histone proteins.

Duplicated chromosome - undergone DNA replication in preparation for cell division, containing two identical copies (sister chromatids) joined by a centromere.

Homologous chromosomes: a pair of chromosomes that have the same size, shape, and genes at the same locations.
- one is inherited from each parent
- displayed using a karyotype (display of the number and appearance of the chromosome or an organism).

DNA IN HUMANS
- each cell has 46 chromosomes (23 pairs)
- 22 are called autosomes (not sex chromosomes)
- 23rd pair depicts the sex, Male: XY, Female XX

Question 4

Explain DNA in Eukaryotes (mitochondria and chloroplast)

Answer 4

• similar to prokaryotic DNA -> lends support to the endosymbiotic theory which proposes that eukaryotic cells were formed when a bacterial cell was ingested by another primitive prokaryotic cell

Question 5

DNA in prokaryotes

Answer 5

• single, cellular chromosome in the cytoplasm.
• sometimes additional small rings of DNA called plasmids (contain non-essential genes and can replicate independently of the main chromosome) are present
• haploid

Haploid: single set of chromosomes (non-homologous chromosome)
Diploid: two sets of chromosomes (homologous chromosomes)

Question 6

What are the differences between Prokaryotic DNA and Eukaryotic DNA?

Answer 6

Prokaryotic
- found in the cytoplasm
- small number of genes
- organised into a single chromosome
- naked (no histones (protein))
- circular

Eukaryotic
- Found in the nucleus, mitochondria, and chloroplasts.
- Large number of genes
- Organised into many chromosomes
- associated with histones
- linear

Question 7

What is the Nucleotide composition?

Answer 7

• DNA is made of subunits called nucleotides (organised into strands that are wound around each other to form a double helix)

Nucleotides contain:
- five - carbon sugar (Deoxyribose in DNA, ribose in RNA)
- negatively charged phosphate group
- nitrogenous base DNA (A, C, G, T), RNA (A, C, G, U)

Question 8

What are the complimentary base pairings?

Answer 8

Adenine + Thymine (A+T)
Cytosine + Guanine (C+G)

At The Gold Coast

Question 9

What are Hydrogen Bonds?

Answer 9

• Between base pairs, there is a weak hydrogen bond formed.
• hydrogen bonds hold the double helix together

C & G = 3 hydrogen bonds
A & T = 2 hydrogen bonds

Question 10

What is RNA?

Answer 10

• carries out the instructions from the DNA: It copies the DNA to ensure the relevant proteins are made.
• composed of a single chain of nucleotides (single-stranded, NO double helix)
• contains the base Uracil (U) instead of Thymine -> complementary pair: U & A.
• Contains ribose sugar (as opposed to DNA’s Deoxyribose)

There are three concepts involved in RNA
1. mRNA (messenger RNA): acts as a blueprint, carrying genetic instructions from DNA in the nucleus to the ribosome (where protein is created).
2. tRNA (transfer RNA): brings the correct, specific amino acids to the ribosome and matches them to the mRNA instructions
3. rRNA (ribosomal RNA):This is the core of the ribosome, where proteins are made. rRNA helps form the structure of the ribosome and catalyzes the formation of bonds between amino acids, which is what actually assembles the protein chain.

Question 11

What is DNA replication?

Answer 11

When cells replicate their DNA to ensure each daughter cell receives the instructions for the proper functioning of that cell before undergoing cell division (for growth, repair, reproduction) also known as interphase

Question 12

What is the process of DNA replication?

Answer 12

Direction: 5’ to 3’
OCcurs in a forwards direction

1. DNA helicase (enzyme) unzips the double helix DNA molecule by breaking the weak hydrogen bonds between the nucleotides = exposing the bases (small portions of DNA is ‘unzipped’ one at a time.
2. The replication fork (junction between the unwound single strands of DNA and the intact double helix) moves along the DNA so that there is a continuous unwinding of the parental strands.
3. When the bases are exposed, Primase (enzyme) begins the process, produces a small piece of RNA called primer (the starting point)
4. DNA polymerase (enzyme) binds to the primer, and creates new strands that are identical to those that already exist (complimentary) -> adds these new identical strands to the exposed bases to reform a double helix from the 5’ end to the 3’..
5. there are now two double helix DNA molecules - each with a parent strand and a new strand.