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Biology Module 2 > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q

DRAW A NUCLEOTIDE

A

DRAW IT

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2
Q

DRAW A NUCLEOTIDE CHAIN

A

DRAW IT

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3
Q

Describe Nucleotide

A
  • Biological molecules that participate in almost all biochemical processes
  • They are phosphate esters of pentose sugars, the nitrogenous base is linked to the Carbon 1 of the sugar residue, and a phosphate groups is linked to Carbon 5 or Carbon 3 of the sugar residue by covalent bonds formed by condensation reactions
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4
Q

What are the uses of Nucleotides

A
  • Form monomers of nucleic acids, DNA and RNA, in RNA the nucleotide pentose sugar is ribose, in DNA the nucleotide pentose sugar is deoxyribose
  • Become phosphorylated nucleotides when they contain more than one phosphate group e.g. – ADP and ATP is an energy-rich end-product of most energy-releasing biochemical pathways – used to drive most energy-requiring metabolic processes in cells
  • Regulates many metabolic pathways
  • May be components of many coenzymes – adenine nucleotides are components of the coenzyme NADP, this is used in photosynthesis and of NAD which is a coenzyme used in respiration and of FAS and coenzyme A these are used in respiration
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5
Q

where is DNA found in eukaryotic cells

A

found in the nuclei

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6
Q

Where is the DNA found in prokaryotic cells and viruses

A

found in the cytoplasm

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7
Q

What does DNA carry

A
  • Herdiatory material and carriers coded instructions for the development and functions of all organisms
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8
Q

DNA is an important …

A

Macromolecule

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9
Q

Describe the structure of DNA

A
  • Polymer made up of many repeating monomeric units called nucleotides,
  • A molecule of DNA consist of two polynucleotide strands
  • Strands run in opposite direction so as antiparallel
  • Each DNA nucleotide consist of a phosphate group, a five carbon sugar called deoxyribose and one of four nitrogenous bases
  • The covalent bond between the sugar residue and the phosphate group in a nucleotide is also called a phosphodiester bond – these are bonds are broken when polynucleotides break down and are formed when polynucleotides are synthesised
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10
Q

what are the purine bases

A

Adenine or Guanine

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11
Q

What are the pyrimidine bases

A

Thymine or Cytosine

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12
Q

What is the difference between purine and pyrimidine

A

Purine has two rings whereas pyrimidine has one ring

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13
Q

what are the complementary bases

A

A-T - by two hydrogen bonds

C-G - by three hydrogen bonds

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14
Q

Describe the role that hydrogen bonds play in the structure of DNA

A
  • Two antiparallel DNA strands are joined together by hydrogen bonds between the nitrogenous bases
  • Purine always pairs with a pyrimidine this gives equal size rungs on the DNA ladder – these then twist around an imaginary axis and gives it its double helix coil giving the molecule stability
  • Hydrogen bonds allow the molecule to unzip for transcription and replication
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15
Q

Describe the antiparallel sugar phosphate backbones

A
  • Opposite direction of the two strands refers to the direction that the third and fifth carbon molecules are facing
  • The 5’ end of the molecule is where the phosphate group is attached to the fifth carbon of the deoxyribose sugar
  • The 3’ end is where the phosphate group is attached to the third carbon of the deoxyribose sugar
  • The rungs of the ladder consist of the complementary base pairs joined by hydrogen bonds
  • Molecule is stable and the integrity of the coded information within the base sequences is protected
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16
Q

How is DNA organised in an Eukaryotic cell

A
  • The DNA content or the genome is in the nucleus
  • Each molecule of DNA is tightly wound around histone proteins into chromosomes
  • Each chromosome is therefore one molecule of DNA
  • There is a loop of DNA without the histone proteins inside the mitochondria and chloroplasts
17
Q

How is DNA organised in a prokaryotic cell

A
  • DNA is in a loop within the cytoplasm and is not enclosed in an nucleus
  • Not wound around histone protein and is describe as naked
18
Q

How is DNA organised in a virus

A

it contains DNA in the form of a loop of naked DNA

19
Q

Describe the process of semi-conservative replication

A
  1. The double helix unwinds its self but not all at once this is catalysed by a gyrase enzyme
  2. The hydrogen bonds between the nucleotide bases are broken this is catalysed by DNA helicase and now there are two single strands of DNA exposed with nucleotide bases
  3. Free phosphorylated nucleotides present in the nucleoplasm within the nucleus are bonded to the exposed bases following complementary base pairing rules
  4. The enzyme DNA polymerase catalyses the addition of the new nucleotide bases in the 5’ to 3’ direction, to the single strands of DNA it uses each single strand of unzipped DNA as a template
  5. The leading strand is continuously synthesised whereas the lagging strands which is in fragments are later joined, this is catalysed by ligase enzymes
  6. Hydrolysis of the activated nucleotides to release phosphate groups sully the energy to make phosphodiester bonds between the sugar residue of one nucleotide and the phosphate group of the next nucleotide
    - The product of the replication is two DNA molecules identical to each other and the parent molecule – contains one old strand and one new strand therefore its semi-conservative
    - Loops of DNA within prokaryotes inside mitcohodria and chloroplasts also replicate semi-conservatively
20
Q

When does DNA self replicating happen

A

interphase - this is the moment before the cell divides, the DNA in mitochondria and chloroplasts also replicate and divide

21
Q

What is the first step of semi-conservative replication

A

firstly they are joined together at the centromere and form two sister chromatids

22
Q

Describe the Meselson and Stahl experiment - evidence for semi-conservative replication

A
  • They grew bacteria E.coli for 14 generations in a medium which was has a heavy isotope of nitrogen 15N, this contains an extra neuron in every atomic nucleus – after 14 generations most of the DNA would be heavy as it would contain 15N
  • They then transferred the E.coli into a medium which contained normal 14N, they left them there long enough to undergo one replicaton
  • The DNA from these bacteria after one division was found to be hybrid DNA – showed that DNA does not replicate conservatively as this would have produced a heavy strand and a light strand
  • Bacteria were allowed to divide once more and DNA was extracted and put in a centrifuge, this produced two bands of DNA one hybrid and one light showing that replication is semi-conservative and not dispersive
23
Q

Describe mutations

A
  • During DNA replication errors may occur and wrong nucleotide may be inserted
  • This could change the genetic code
  • Enzyme proofread and edit out mutations this reduces the rate that mutations are produced
  • Genes have changes to their nucleotide sequence – different versions of a particular gene are called alleles
  • Not all mutations are harmful
24
Q

How is RNA different from DNA

A
  • The sugar molecule in each nucleotide is ribose
  • The nitrogenous base uracil which is pyrimidine replaces the pyrimidine base thymine
  • The polynucleotide chain is usually single stranded
  • The polynucleotide chain is shorter
  • There are three forms of RNA – messenger RNA (mRNA) transfer RNA (tRNA) and ribosomal RNA (rRNA)
25
Q

Describe the process of transcription

A
  1. A gene unwinds and unzips
  2. Hydrogen bonds between complementary nucleotide bases break
  3. The enzyme RNA polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired bases; this is called the template strand
  4. A length of RNA that is complementary to the template strand of the gene is produced therefore is a copy of the other DNA strand this is called the coding strand
  5. The mRNA now passes out of the nucleus through the nucleus envelope into the cytoplasm and attaches to the ribosome
    - Ribosomes are made in the nucleolus in two smaller subunits – they pass separately out of the nucleus through pores in the nuclear envelope and come together to form the ribosome – magnesium ions help to bind the two subunits together - made of ribosomal RNA and protein
26
Q

Describe the process of translation

A
  • Transfer RNA molecules are made in the nucleolus and pass out of the nucleus into the cytoplasm – they are single stranded polynucleotides but can twist into a hairpin shape – at one end is a trio of nucleotide bases that recognises and attaches to a specific amino acid
  • At the loop of the hairpin there is another triplet of bases called an anticodon that are complementary to a specific codon of bases of the mRNA
    1. Transfer RNA molecules bring the amino acids and find their place when the anticodon binds by temporary hydrogen bonds to the complementary codon on the mRNA molecule
    2. As the ribosome moves along the length of the MRNA it reads the code, when two amino acids are adjacent peptide bonds form between them
    3. Energy in the form of ATP is needed for polypeptide synthesis
    4. The amino acid sequence for the polypeptide is therefore determined by the sequence of DNA triplets for nucleotide bases on the length of DNA
    5. After the polypeptide is assembled the mRNA breaks down these are recycled into new lengths of MRNA with different codon sequences
    6. Newly synthesised polypeptide is helped by chaperone proteins in the cell to fold correctly into its tertiary structure to carry out its function
27
Q

What does a gene contain

A

each gene contains a code that determines the sequence of amino acids in a polypeptide or protein

28
Q

What does the DNA base triplet determine

A
  • Within each gene there is a sequence of DNA base triplets that determine the amino acid sequence or primary structure of a polypeptide – in the primary structure is correct then it will fold correctly and be held in its tertiary structure or shape therefore will be able to carry out its function
29
Q

How do genes pass out of the nucleus

A
  • Instructions in the genes on chromosomes cannot pass out of the nucleus therefore a copy of each gene has to be transcribed into a length of mRNA, In this form the base triplets/codons can pass out of the nucleus to the ribosomes this ensures that the coded instructions are translated and the correct protein is made
30
Q

Describe the nature of the genetic code

A
  • The Genetic code is near universal because in almost all living organisms the same triplet of DNA bases codes for the same amino acid
  • The genetic code is described as degenerate – all the amino acids except methionine and tryptophan, there is more than one base triplet – reduces the effect of point mutations as a change in one base of the triplet could produce another base triplet that still codes for the same amino acid
  • The genetic code is non-overlapping – it is read from a fixed point in groups of three bases, if a base is added or deleted then it causes a frame shift, as every base triplet after that and hence every amino acid coded for is changed

Biology Module 2 (17 decks)

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