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Biology Unit 2 > DNA & Meiosis > Flashcards

DNA & Meiosis Flashcards

1
Q

What three components make up a nucleotide?

A
  • deoxyribose (sugar)
  • a phosphate
  • a base (either single ringed: C & T, or double ringed: A & G)
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2
Q

Why type of reaction forms a nucleotide?

A

Condensation

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3
Q

What are the pairs of bases?

A

Adenine two H+ bonds Thymine

Guanine three H+ bonds Cytosine

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4
Q

Why are the quantities of A&T and G&C always the same?

A

Because they are bonded in complementary pairs

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5
Q

What other element is in the base group of a nucleotide?

A

Nitrogen

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6
Q

What are the uprights & rungs of the DNA ladder made from?

A 
Rungs = pairs of bases
Uprights = deoxyribose-phosphate molecules
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7
Q

How are polynucleotides formed?

A
  • condensation reaction between deoxyribose sugar & phosphate between two different nucleotides
  • water lost = phosphodiester bond formed
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8
Q

What is the name of the structure of DNA?

A

Double-helix structure

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9
Q

How do different DNA molecules differ from one another if there is always a deoxyribose sugar, phosphate & the 4 bases in each one?

A

Different proportions of bases ( ratio between pairs varies from species to species)

Different sequence of bases

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10
Q

How is the DNA molecule adapted to carry out its functions?

A
  • stable: pass through generations without change
  • two polynucleotide chains are joined by H+ bonds = separate in DNA replication
  • large molecule = carries a lot of genetic info
  • base pairs protected within helical structure from outside chemicals
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11
Q

How many bases make up an amino acid?

A

Three base pairs - triplet code

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12
Q

How are different amino acids made?

A

Different combination & sequence of bases

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13
Q

What is a gene?

A

Genes are sections of DNA and are found on chromosomes. They code for proteins (polypeptides) as the contain the instructions (specific base sequences) to make them

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14
Q

What is an intron and exon?

A

Intron: Section of non-coding DNA that can occur within genes as multiple repeats, are removed in protein synthesis
Exon: opposite

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15
Q

Give three features of the triplet code

A
  • the code is non-overlapping
  • it’s a Degenerate Code, because most amino acids have more than one triplet code
  • three triplet codes don’t code for any amino acid: Stop Codes mark the end of a polypeptide chain
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16
Q

Besides introns what is another region in genes that don’t code for amino acids?

A

Multiple repeat regions (DNA sequences that repeat over and over)

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17
Q

What’s the difference between prokaryotic & eukaryotic DNA?

A
  • prokaryotic = DNA plasmids (rings)

- eukaryotic = linear DNA (form chromosomes)

18
Q

What a phenotype?

A

The characteristic produced by a gene

19
Q

What is a genotype?

A

A type of gene (codes for the phenotype)

20
Q

What is the sequence that shows how genes determine our phenotype?

A
  1. DNA sequence determines amino acid sequence
  2. Protein/ enzyme formed
  3. Enzymes control metabolic pathways
  4. Metabolic pathways help determine nature & development
21
Q

What is an allele?

A

A form of a gene, different alleles code for slightly different versions of the same characteristic

22
Q

How many pairs of chromosomes do humans have?

A

23 pairs

23
Q

What is the name of a single thread of a chromosome?

A

Chromatid

24
Q

What are pairs of matching chromosomes called?

A

Homologous pairs

25
Q

What makes two chromatids a homologous pair?

A
  • same genes (but different alleles)

- same size

26
Q

How many molecules of DNA is in one chromatid?

A

Only one - but the DNA molecule is extremely long

27
Q

What joins two chromatids together to form a chromosome?

A

The centromere

28
Q

What is the diploid number of chromosomes in a human cell?

A

46

29
Q

What would happen if there was a mutation affecting the sequence of bases in a gene that codes for an enzyme?

A
  • may not fold up properly = wrong active site shape
30
Q

What is the name given to the position on a chromosome that a particular allele occupies?

A

The locus

31
Q

How are new alleles of a gene produced?

A

Mutations

32
Q

How can mutations affect enzyme activity?

A

They prevent it from forming it’s correct shape

33
Q

What is meant by semi-conservative replication

A

Producing two copies of DNA, that each contained one of the original strands and one new strand

34
Q

What does meiosis do?

A

Produces gametes / 4 non-identical daughter cells

35
Q

Does meiosis produce diploid or haploid daughter cells - and why?

A

Haploid - so that when gametes fuse there is not too much DNA

36
Q

What are the 4 stages of Meiosis One (the first division)?

A
  • prophase I: nuclear membrane disappears, spindle fibers, centrioles move to opposite poles, chiasmata form
  • metaphase I: chromosomes line up in their homo pairs along equator, independent assortment occurs
  • anaphase I: spindle fibers contract pulling chromosomes to opposite poles
  • telophase I: cell splits = two haploid cells produced
37
Q

What are the 3 stages of Meiosis Two (second division)?

A
  • metaphase II: chromosomes line up on equator
  • anaphase II: spindle fibers contract & pull chromatids (half of chromosomes) to opposite poles, both cells split
  • telophase II: 4 unique haploid cells produced (¼ mass of original DNA)
38
Q

What happens when the chiasmata form in Prophase I?

A

Chromatids wrap around each other & exchange genetic info

39
Q

What is independent assortment?

A

Chromosomes line up along equator in random order

40
Q

What is stop/start codon?

A

There are only 3 combinations in the work of 3 base pairs, ATT, GCC, TGC, (triplet codes) that do not code for any amino acid, and so act as the full stop between different amino acids.

41
Q

What are two ways in which genetic variation is created through meiosis?

A
  • independent assortment

- chiasmata cross over

42
Q

What is a nucleotide?

A

A form basis of DNA that join together

Biology Unit 2 (11 decks)

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