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Biology > * Molecular genetics (Ch26) > Flashcards

* Molecular genetics (Ch26) Flashcards

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1
Q

Structure of chromosome

A
  • DNA + proteins
  • Long thread of DNA molecule wraps around proteins, forming nucleosomes, which then further coils up to form chromatin thread
  • Chromatin thread further condenses to form chromosome
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2
Q

Significance of organization how DNA is organized to form a chromosome

A
  • Allow the long chain of DNA to be packed densely
  • DNA molecules are protected by proteins
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3
Q

Structure of DNA

A
  • Nucleic acid made up of nucleotides
  • Two polynucleotide chains coiled as double helix, are parallel to each other and run in opposite directions, held together by complementary pairs of bases bonded by weak hydrogen bonds
  • A pair with T (2 H-bonds)
  • C pair with G (3 H-bonds)

Adenine / Thymine / Uracil / Guanine / Cytosine

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4
Q

Role of DNA

A
  • Carries the genetic code controlling synthesis of proteins, hence metabolic activities and characteristics of organisms
  • Capable of self-replication, important for increase in cell number during growth and reproduction
  • Mutation can occur to produce variation
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5
Q

Genetic code

A
  • Triplet code
  • Degenerate code: a single amino acid may be coded by more than one triplet of bases (4 different nucleotides form a triplet, 4^3 = 64 combination of triplet codes -> only 20 amino acids, some amino acids have more than 1 triplet code)
  • Non-overlapping code
  • Universal code: the same triplet code works for the same amino acids in all organisms
  • Nonsense triplets
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6
Q

Features of DNA molecule enable it to function as material for inheritance

A
  1. DNA can store a lot of genetic information because it is a long polymer of nucleotides
  2. Degenerate code: a single amino acid may be coded by more than one triplet of bases (4 different nucleotides form a triplet, 4^3 = 64 combination of triplet codes -> only 20 amino acids, some amino acids have more than 1 triplet code)
  3. Different sequence of nucleotide triplets along the DNA molecule represent specific sequence of amino acids in a polypeptide, huge variations of sequence allow a lot of genetic information to be stored
  4. Nitrogenous bases pair up through complementary base pairing
  5. Hydrogen bonds of DNA can be easily broken and reformed, allowing transcription and DNA duplication takes place
  6. The two strands of nucleotides form a helical structure, forming a stable structure for protection of genetic information
  7. Strong sugar-phosphate backbone prevents the base sequence of a gene from swapping
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7
Q

Process of protein synthesis (framework)

A
  1. DNA carries genetic information coding for proteins
  2. Transcription takes place in nucleus to produce mRNA
  3. mRNA transported to ribosome for translation
  4. Polypeptide form in translation
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8
Q

Transcription

A
  1. RNA polymerase attaches to the start point of a gene on the DNA
  2. Genetic information on DNA transcribed to a mRNA molecule, one of the DNA strands acts as template
  3. mRNA molecules are formed according to the base sequence on DNA template by complementary base pairing
  4. mRNA formed is released when RNA polymerase reaches the stop codon
  5. mRNA leaves the nucleus
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9
Q

Translation

A
  1. mRNA attaches to ribosome
  2. tRNA carrying specific amino acid with anticodon complementary to the codon on mRNA attach to ribosome
  3. Peptide bonds form between adjacent amino acids, forming polypeptide
  4. Completed polypeptide is released from the ribosome
  5. Coiling and folding of polypeptide due to intramolecular bonds gives the final 3D conformation of protein
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10
Q

DNA vs RNA

A

DNA
- ATGC
- Double helix
- Deoxyribose
- One type

RNA
- AUGC
- Single polynucleotide strand
- Ribose
- 3 types: mRNA, tRNA , rRNA

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11
Q

Transcription vs Translation

A

Transcription
- Template: one of the DNA strands
- Involves RNA polymerase
- Occurs in nucleus
- Monomer: RNA nucleotide
- Produces mRNA

Translation
- Template: mRNA
- Involves ribosomes
- Occurs in cytoplasm
- Monomer: amino acids
- Produces polypeptides

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12
Q

How genetic information on DNA controls cellular activities and morphology

A
  1. Genetic information on DNA is conveyed by sequence of bases in polynucleotide chain
  2. Genetic information on DNA is first transcribed to mRNA molecule, one of the DNA strands acts as template
  3. mRNA molecules formed according to base sequence on DNA template by complementary base pairing
  4. mRNA containing codons for translation moves out of the nucleus and attaches to the ribosomes in cytoplasm
  5. Free amino acid is activated by joining to tRNA using ATP
  6. tRNA carrying specific amino acid with anticodon complementary to codon on mRNA attaches to ribosome
  7. Peptide bond forms between adjacent amino acids, forming polypeptide
  8. Coiling and folding of polypeptide gives 3D conformation of protein
  9. Functional proteins (enzyme, hormone, carrier proteins) control cellular activities
  10. Functional proteins determine morphology
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13
Q

Why identical cells in zygote can develop into different cells

A
  • Different subsets of genes are expressed in different cells
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14
Q

Mutation

A
  • Mutation is the sudden and permanent change of genetic material
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15
Q

Gene mutation

A
  1. Insertion
  2. Deletion
  3. Inversion
  4. Substitution
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16
Q

Effect of insertion / deletion

A
  • Addition / Loss of a nucleotide shifts the subsequent nucleotide sequence
  • The whole chain of amino acids that follows will be completely different from the original one
  • Amino acid sequence produced folds to different shape
  • A completely different protein is produced, losing its original functions
17
Q

Effect of substitution / inversion

A

No effect:
- There is only a change in one triplet code
- The new code formed may be degenerated
- No change to original polypeptide

  • There is only a change in one triplet code
  • The new code formed encodes another amino acid which is not involved in the formation of active site
  • After coiling and folding of the polypeptide, the 3D conformation of active site of protein remains the same

Have effect:
- The triplet code involved changes to a stop codon, stopping the translation process at the point of mutation
- Mutated gene cannot be translated completely
- Amino acid chain formed is shorter than original one, which coils and folds to a different protein with different 3D conformation, which may be smaller in size / non-functional

  • The new code formed encodes another amino acid involved in the formation of active site, altering the 3D conformation of active site
  • Enzyme-substrate complex cannot be formed
18
Q

Sickle cell anaemia

A
  • Abnormal haemoglobin formed in red blood cells has low oxygen-carrying capacity
  • Sickle shaped red blood cells block blood vessels easily
19
Q

Changes in number of chromosomes

A
  • During formation of gametes by meiosis, the homologous pair of a certain chromosome fail to separate
  • Both chromosomes will be present / absent in the gamete formed
20
Q

Down Syndrome

A
  • During formation of gametes by meiosis, homologous pair 21 fail to separate
  • Both chromosomes will be present in the gamete formed, when this gamete fuses with a normal gamete, a zygote with an extra chromosome 21 is produces
21
Q

Causes of mutation

A
  1. Spontaneous mutation
  2. Induced mutation (by mutagens: radiation, chemicals, viruses)
22
Q

Importance of variations

A
  • Variations lead to different niches, reducing competition
  • Cope with environmental changes: provides a range of variants within the same species for natural selection
23
Q
A

Biology (38 decks)

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