3.4.1 DNA, genes and chromosomes Flashcards

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1
Q

Define gene

A
  • a section of DNA located on a fixed site called the Locus
  • contains a specific sequence of bases for the formation of polypeptides and functional RNA (ribosomal and transfer)
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2
Q

What are the three main features of the genetic code?

A
  • universal - the same in almost all organisms
  • non-overlapping - each triplet is read only once
  • degenerate - all but two amino acids have more than one DNA triplet (as there are more possible triplet combos than there are amino acids)
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3
Q

How many different triplets and amino acids are there?

A

64 triplets - there are 20 amino acids so some are coded for by more than one triplet

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4
Q

Define stop code

A

don’t code for any amino acid and mark the end of a chain

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5
Q

Define exon

A

a base sequence which codes for a polypeptide sequence of amino acids

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6
Q

Define intron

A

non-coding sequences (only found in eukaryotes)
- removed during transcription and exons are joined (splicing)

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7
Q

Define non-coding repeats

A

positioned outside of the gene and contain the same base sequence repeated multiple times

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8
Q

Describe the main differences between prokaryotic and eukaryotic DNA

A

Prokaryotic VS Eukaryotic
* in cytoplasm - in nucleus
* circular - linear
* not associated with proteins - associate with histone proteins to form chromosomes
* shorter - longer
* no introns - introns

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9
Q

Describe DNA structure in eukaryotic cells

A
  • DNA is wound around histone proteins - these also support the DNA
  • DNA-histone complex is coiled and coils fold to form loops
  • loops pack to form a chomosome
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10
Q

Describe DNA structure in prokaryotic cells

A

DNA loops condenses via supercoiling

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11
Q

What is DNA like within chloroplasts and mitochondria?

A

similar to prokaryotic cells - short, circular and not associated with histone proteins

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12
Q

Define homologous pair

A

a chromosome pair, one maternal and one paternal , with the same gene loci

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13
Q

Define Allele

A

alternative forms of the same gene (one allele is gained from each parent)
- slightly different base sequences
- different amino acid sequence
- different polypeptide formed

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