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Biology > Molecular Genetics > Flashcards

Molecular Genetics Flashcards

1
Q

What is DNA and what is made up of?

A

it is a molecule that carries genetic information and is made up of deoxyribose sugar molecule, a phosphate group and a nitrogenous base

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2
Q

What is the structure of DNA?

A

DNA exists as a double helix by having 2 polynucleotides coiled around each other in a right handed orientation . They are anti-parallel relative to each other and run in opposite directions

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3
Q

Formation of polynucleotide

A

made possible by condensation reaction which is the removal of one molecule of water between 2 nucleotides, forming a phosphodiester bond (strong covalent bond)which holds the sugar-phosphate ‘backbone’ together. this reaction is catalysed by the enzyme phosphodiesterase and can be repeated between many nucleotides, forming a long chain of nucleotides aka polynucleotide chain.

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4
Q

What are the types of nitrogenous base and what is their function?

A

Adenine, Thymine(pairs together with 2 hydrogen bonds)
Cytosine, Guanine(pairs tgt with 3 hydrogen bonds)
the two polynucleotide strands are held together by complementary bases pairing between these bases.
they form weak hydrogen between them

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5
Q

Importance of hydrogen bonding and base pairing?

A
  1. allows for semi-conservation replication
  2. DNA repair -intact strand can be used as template to guide the repair
  3. Stability of DNA, strong covalent bonds between phosphate and deoxyribose groups ensures that nucleotides stay in each strand
  4. Weak H+ bonds bwteen the two polynucleotide strands allow for easier DNA separation during replication of info
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6
Q

Purpose of large number of hydrogen bonds between complementary base pairing?

A

provide stability for the DNA double helix sturcture

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7
Q

Features of DNA

A

have means to code for and store genetic info

must be able to make exact copies of itself

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8
Q

DNA structure and function

A
  1. Specific sequence of bases = information in the form of code to synthesise specific proteins
  2. Long = store more information
  3. Double helix structure with the base pairs within the helical cylinder of the sugar-phosphate backbone = provides stability+protects information to some extent from being corrupted by external chemical and physical
    forces
  4. base pairs are held by hydrogen bonds= weak bonds broken more easily, replication of information can occur more easily
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9
Q

Principles of the semi-conservation replication?

A
  1. unwinding and separation of two DNA strands
  2. each strand is used as a template for complementary base pairing
  3. the daughter molecule contains one of the original strands and one newly-synthesised strand
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10
Q

What is a gene?

A

it is a segment of DNA which codes for a specific polypeptide which will determine a trait of the organism

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11
Q

how do genes affect traits?

A

the nucleotide sequence of the gene will determine the type of polypeptide formed. a polypeptide is built up by the condensation of individual amino acids. amino acids make up a cell protein so the properties of each protein is determined by the type of amino acid involved and the sequence in which they are joined

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12
Q

what is the genetic code?

A

the sequence of bases which will determine the sequence of amino acids that makes up the polypeptide

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13
Q

what are the properties of genetic code?

A
  1. it is made of triplet codes, one triplet code refers to three consecutive nucleotides forming a codon which will code for one amino acid
  2. degenerate so more than one codon may code for the same amino acid
  3. universal, the same codon codes for the same amino acid in almost all organisms
  4. non-overlapping, so each base of the sequence is read once only
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14
Q

What is genetic mutation?

A

It is a sudden random change in the structure of gene (ie sequence of bases) or in the chromosome number or in the chromosome structure
all fo these may alter the codon so it will code for a different amino acid, resulting a different polypeptide formed and subsequently, a different primary structure and then a different tertiary structure formed

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15
Q

what is genetic mutation caused by?

A
  1. occur spontaneously during DNA replication

2. certain conditions and chemicals may change sequence of bases

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16
Q

what is one example of gene mutation?

A

Sickle-cell anaemia
one of the genes coding for the amino acid sequence of a part of haemoglobin in rbcs occassionally mutates at one base pair, resulting in the formation of atypical form of haemoglobin which tends to attract other haemoglobin molecules to bind it. this results in sickle shaped rbcs being formed that are less efficient in carrrying oxygen and tend to get stuck together, thereby blocking many smaller capillaries and reducing rate of blood flow . this causes inadequate oxygen delivery to cells

17
Q

what is one example of chromosomal mutation?

A

Down’s syndrome
a genetic disorder that causes lifelong mental retardation, developmental delays and other problems.
this occurs when individual chromosome do not segregate normally during anaphase of meiosis, resulting in an extra copy of chromosome 21, which will increase the number of chromosomes from the normal 46 to 47 in a somatic cell.

18
Q

Describe RNA

A
  • it is single stranded and composes only one polynucleotide stand
  • ribose sugar which is a 5 carbon sugar
  • made in nucleus, located in the cytoplasm
  • uracil instead of thymine
  • 3 types of RNA
19
Q

what are the different types of RNA?

A 
Transfer RNA (tRNA)
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
20
Q

Functions of tRNA

A

it carries amino acids to the ribosomes and arranges them along the mRNA where they would linked by peptide bonds. it has an anticodon on its “tip” and corresponding amino acid on its “tail”. it links the correct amino acid to its corresponding mRNA codon through codon-anticodon interaction.
each tRNA is specific to the amino acid it binds

21
Q

Functions of mRNA

A
  • contains codons that codes for the peptide sequence.
  • transfers genetic information necessary for protein synthesis from DNA in the nucleus to ribosomes in the cytoplasm.
  • has bases arranged in triplets which directs the formation of protein by ribosomes
22
Q

Functions of rRNA

A

proteins from cytoplasm are assembled with rRNA into large and small ribosomal subunits which leave the nucleus and into the cytoplasm where the subunits assemble into ribosomes.

23
Q

Transcription

A

occurs in the nucleus of the cell:

  1. Helicase breaks the hydrogen bonds holding the double helix of DNA, exposing the DNA bases
  2. RNA polymerase recognises and binds to only one of the DNA strands which is the template strand at the promoter site
  3. RNA polymerase works in a 5’ to 3’ direction and forrms a pre-mRNA transript by matching free RNA nucleotides with the template strand by complementary base-pairing and by catalysing the condensation reaction between the sugar and phosphate groups of adjacent RNA nucleotides
  4. The DNA double helix reforms when the polymerase moves away
  5. Transcription ends whent he RNA polymerase reaches the terminator site and then detaches itself from the DNA strand and pre-mRNA is formed
24
Q

Translation

A

occurs in the cytoplasm of the cell, ribosomes are needed:

  1. mRNA binds with the small ribosomal subunit at the attachment site
  2. the first three exposed codons of the mRNA that make up the start codon are always AUG which can be removed after synthesis if it does not make up part of the polypeptide
  3. The tRNA molecule with anticodon UAC forms H+ bonds with AUG through complementary base pairing
  4. the amino acid methionine is attached to this tRNA and can be removed after synthesis if it does not make up part of the finished polypeptide
  5. another tRNA molecule bonds with the next 3 bases of the mRNA molecule, bringing another amino acid alongside methionine.
  6. an ezyme from the large ribosomal subunit, peptidyl transferase, catalyses the formation of peptide bonds between the 2 amino acids through condensation reaction
  7. the ribosome continues to move along the mRNA in a 5’ to 3’ direction and the next codon is read, resulting in a growing chain of polypeptide attached to the new incoming amino acid upon formation of a peptide bond between the dipeptide and new amino acid
  8. The first tRNA molecule leaves the ribosome without the amino acid
  9. this continues until the ribosome reaches the stop codon which can be UAA, UAG and UGA which will stop attracting tRNA molecules.
  10. the completed polypeptide is then released
25
Q

What is genetic engineering?

A

it is the transfer of genes between organisms, inserting foreign genes from another organsim results in a transgenic organism

26
Q

What is plasmid?

A

it is a small piece of DNA and is also known as vector

27
Q

Human insulin production

A
  1. isolate the human insulin gene by using restriction enzymes to cut it out from the DNA and produce sticky ends
  2. use the same restriction enzymes to cut the bacterial plasmid to produce complementary sticky ends
  3. Mix the the cut plasmid with the DNA fragment containing the insulin gene
  4. Add DNA ligase to join the two together through complementary base pairing to produce a recombinant plasmid
  5. Mix/ reintroduce the recombinant plasmid into the bacteria
  6. apply heat or electric shock to open up pores in the cell surface membrane of the bacteria to allow the recombinant plasmid to enter
  7. this is then followed by mass culture of the bacteria in fermentors to allow it to multiply and produce insulin
  8. extraction and purification of insulin
28
Q

Creation of an insect-resistant tomato plant

A
  1. cut the gene
  2. insert the gene into a vector with a selectable antibiotic resistance marker gene
  3. allow the vector in bacteria to multiply
  4. coat tungsten/gold particles with the DNA vectors and load it onto a teflon bullet
  5. load the bullet into gene gun
  6. shooting the gene gun releases the particles at high velocity so it can penetrate the plant cell
  7. the vector enters the plant cell and may be incorporated into the plant genome
  8. the cells are placed on selective antibiotic media and only cells that have incorporated the vector will grow
  9. these cells are transferred to medium containing plant growth factors.
29
Q

Genetic engineering benefits

A

genetically altered to be resistant to droughts, pest etc increases yield of crops
genetically altered to give maximum output at minimum cost
treatment of diseases, food designed to meet specific goal

30
Q

Genetic engineering hazards

A

loss of biodiversity: GM crops produce toxins that kills insects
insects may adapt and develop resistance against these toxins
GM seeds may be infertile, have to buy more seeds, put poorer farmers at a disadvantage. prices of see not regulated, poorer farmers cannot afford or make a living
accidental production of harmful toxins in crops
social divide, religious concerns

Biology (12 decks)

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