DNA

Question 1

What is the polymer of DNA?

Answer 1

Nuclei acid

Question 2

What’s the monomer of DNA?

Answer 2

Nucleotide

Question 3

What bonds join the nucleotides to another nucleotide?

Answer 3

Phosphodiester bonds.

Question 4

What’s a nucleotide made up of?

Answer 4

A phosphate group, (glycosidic bond) a deoxyribose pentose sugar and (ester bond) a nitrogenous organic base

Question 5

Who is credited with working the structure of DNA?

Answer 5

Watson and Crick.

Question 6

DNA’s structure?

Answer 6

It is a double helix, the two chains running anti parallel with each other. A purine bonds with a pyrimidine otherwise the helix structure would not be even. It has a sugar phosphate backbone.

Question 7

What are the 4 nitrogenous bases and there pairing?

Answer 7

Adenine and Thymine join with 2 hydrogen bonds. Guanine and Cytosine join with 3 hydrogen bonds.

Question 8

What are A and G?

Answer 8

Purines, a doubled ringed structure.

Question 9

What are C and T?

Answer 9

Pyrimidines, a single ringed structure.

Question 10

Why is DNA stable?

Answer 10

So information can be passed down generations accurately.

Question 11

Why does DNA have weak hydrogen bonds?

Answer 11

As it allows for separation when copying for protein synthesis.

Question 12

Why is DNA so long?

Answer 12

As it can fold extensively to store a large amount of information into a very small space.

Question 13

Why does DNA have hydrogen bonds inside it?

Answer 13

The helix protects pairings from from some chemical and physical forces. The phosphate sugar backbone protects this.

Question 14

Why does DNA have a variation in its code?

Answer 14

The small variations in the code decided by the order of the bases gives a simple but numerous code, the variations allow for genetic variation.

Question 15

Why does DNA have base pairing?

Answer 15

Allows copying for DNA and replication to RNA.

Question 16

What does DNA contain?

Answer 16

The hereditary material is responsible for passing on genetic information, it carries the genetic code that controls protein synthesis. Many proteins are enzymes so therefore the DNA can control the development, structure and function of the cell.

Question 17

How does DNA replicate?

Answer 17

By the semi-conservative model, half is conserved.

Question 18

What is required for semi-conservative replication of DNA?

Answer 18

4 types of nucleotide, DNA polymerase and helicase and ATP.

Question 19

How does the semi-conservative model of DNA replication occur?

Answer 19

• It starts of as a double strand.
• an enzyme DNA helicase cause the two strands to separate. The DNA helicase breaks the hydrogen bonds that are linking the base pairs.
• as a result the double helix is separated into two strands and unwinds. Each exposed polynucleotide strand acts as a template to which complementary nucleotides are attached.
• energy is needed to activate these nucleotides. Activated nucleotides are joined together by the enzyme DNA polymerase.
• each of the new DNA molecules contains on of the original strands, these new DNA strands are called daughter DNA.

Question 20

What was the possible hypothesis for DNA replication before the semi-conservative model?

Answer 20

The conservative model.

Question 21

What is the conservative model for DNA replication?

Answer 21

The miscues forms would be one entirely new DNA strand and one original strand.

Question 22

Who set up and experiment to test the semi-conservative model?

Answer 22

Meselsohn and Stahl.

Question 23

Meselsohn and Stahl’s experiment?

Answer 23

They knew bases contained nitrogen and that there were two forms of nitrogen, normal nitrogen N14 and heavy nitrogen N15. They knew bacteria would use nitrogen to form new DNA. Control 1 was a bacteria grown in a N14 medium which had DNA made of light nitrogen, when this DNA is isolated, suspended and centrifuged its floats to the top. Control 2 had bacteria grown in a N15 medium and had DNA made of heavy nitrogen, when this DNA is isolated, suspended and centrifuged is sinks to the bottom. In the experiment N15 bacteria is grown it’s then transferred to N14 one generation, then 2 generations in N14 and then 3 generations in N14. The new DNA formed should have one original strand and one new strand if formed by semi-conservative replication. This is evidence that DNA replicates through the semi conservative replication.

Question 24

Define chromosomes?

Answer 24

A length of DNA tightly coiled. They are only visible during cell division, each chromosome is one molecule of DNA mech species has a specific number of chromosomes e.g. in humans the diploid number is 46 and haploid number is 23. Daughter cells contain an exact copy of the instructions in the parent cell. When visible DNA has replicated itself. The DNA replicas are called sister chromatids which end up in the daughter cells.

Question 25

Define histone?

Answer 25

Proteins which chromosomes coil around.

Question 26

Define gene?

Answer 26

Specific sections of DNA that code for specific polypeptides and functional RNA.

Question 27

Define allele?

Answer 27

Different variations of the same gene.

Question 28

Define gene locus?

Answer 28

The fixed position of a gene on a particular strand of DNA.

Question 29

The genetic code?

Answer 29

The existence of the triplet code was confirmed by Francis Crick in 1961. It is degenerate, each amino acid is coded for by one than one triplet. A triplet means that 3 bases of DNA codes for a specific amino acid. It is universal and found in most living organisms. It is non-overlapping and is always read in in direction and in triplets. The same triplets always start and a to the strand of DNA.

Question 30

Evaluate the genetic code?

Answer 30

The base sequence allows different information to be stored, it is double stranded to allow for replication. It has a sugar phosphate backbone for strength and its long to store a lot. It is helical so it is compact and has hydrogen bonds to allow unzipping.

Question 31

Define exon?

Answer 31

Sections of DNA within a gene that code for an amino acid.

Question 32

Define intron?

Answer 32

In eukaryotes much of the DNA doesn't code for amino acids. There are multiple repeated sequences between genes and introns within a gene which don't code for amino acids and aren't useful.

Question 33

DNA in eukaryotes?

Answer 33

Liner, larger and associated with proteins, forms chromosomes and has 80s (larger) ribosomes.

Question 34

DNA in prokaryotes?

Answer 34

Circular, smaller and not associated with proteins. It forms plasmids and has 70s (smaller) ribosomes.

Question 35

What do chromosomes appear as?

Answer 35

Two threads joined at a single point called the centromere. Each thread is called a chromatid.

Question 36

Homologous chromosomes?

Answer 36

Chromosomes occur in pairs called homologous pairs, the pair are always 2 chromosome that determine the same genetic characteristics. One of the pair is derived from the mother in the egg (maternal) and the other is provided by the father in the sperm (paternal )

Question 37

What forms do genes exist in?

Answer 37

Genes usually exist in 2 different forms called alleles e.g. There are ones for blood type, hair colour and eye colour etc.

Question 38

What caused a gene mutation?

Answer 38

They occur when there is a substitution, deletion or an insertion of a base which effects the whole base sequence.

Question 39

Chromosome mutations?

Answer 39

Changes in the structure or number of whole chromosome. They can arise spontaneously and take two forms; - changes in whole sets of chromosomes - changes in the number of individual chromosomes

Question 40

Changes in whole sets of chromosomes?

Answer 40

This occurs when organisms have 3 or more sets of chromosomes rather than the usual 2. This condition is called polyploidy and most occurs in plants.

Question 41

Changes in the number of individual chromosomes?

Answer 41

Some individual homologous pairs fail to separate during meiosis. This is known as non-disjunction and usually results in a gamete having one more or fewer chromosome. On fertilisation with a gamete that has the normal complement of chromosomes, the resultant offspring have more or fewer chromosomes than normal in all their body cells. An example of non-disjunction in humans is Down's syndrome where individuals have an additional chromosome 21.