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Biology AS > DNA > Flashcards

DNA Flashcards

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1
Q

What is the polymer of DNA?

A

Nuclei acid

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2
Q

What’s the monomer of DNA?

A

Nucleotide

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3
Q

What bonds join the nucleotides to another nucleotide?

A

Phosphodiester bonds.

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4
Q

What’s a nucleotide made up of?

A

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

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5
Q

Who is credited with working the structure of DNA?

A

Watson and Crick.

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6
Q

DNA’s structure?

A

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.

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7
Q

What are the 4 nitrogenous bases and there pairing?

A

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

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8
Q

What are A and G?

A

Purines, a doubled ringed structure.

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9
Q

What are C and T?

A

Pyrimidines, a single ringed structure.

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10
Q

Why is DNA stable?

A

So information can be passed down generations accurately.

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11
Q

Why does DNA have weak hydrogen bonds?

A

As it allows for separation when copying for protein synthesis.

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12
Q

Why is DNA so long?

A

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

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13
Q

Why does DNA have hydrogen bonds inside it?

A

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

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14
Q

Why does DNA have a variation in its code?

A

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.

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15
Q

Why does DNA have base pairing?

A

Allows copying for DNA and replication to RNA.

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16
Q

What does DNA contain?

A

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.

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17
Q

How does DNA replicate?

A

By the semi-conservative model, half is conserved.

18
Q

What is required for semi-conservative replication of DNA?

A

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

19
Q

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

A
  • 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.
20
Q

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

A

The conservative model.

21
Q

What is the conservative model for DNA replication?

A

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

22
Q

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

A

Meselsohn and Stahl.

23
Q

Meselsohn and Stahl’s experiment?

A

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.

24
Q

Define chromosomes?

A

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.

25
Q

Define histone?

A

Proteins which chromosomes coil around.

26
Q

Define gene?

A

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

27
Q

Define allele?

A

Different variations of the same gene.

28
Q

Define gene locus?

A

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

29
Q

The genetic code?

A

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.

30
Q

Evaluate the genetic code?

A

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.

31
Q

Define exon?

A

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

32
Q

Define intron?

A

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.

33
Q

DNA in eukaryotes?

A

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

34
Q

DNA in prokaryotes?

A

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

35
Q

What do chromosomes appear as?

A

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

36
Q

Homologous chromosomes?

A

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 )

37
Q

What forms do genes exist in?

A

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

38
Q

What caused a gene mutation?

A

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

39
Q

Chromosome mutations?

A

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
40
Q

Changes in whole sets of chromosomes?

A

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.

41
Q

Changes in the number of individual chromosomes?

A

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.

Biology AS (42 decks)

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