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Topic 2: Genes and Health > DNA and protein synthesis > Flashcards

DNA and protein synthesis Flashcards

1
Q

What does DNA stand for and what is it made up of? What does it carry?

A
  • deoxyribonucleic acid
  • it is made up of nucleotides
    -it is a chemical made up of 2 long strands called polynucleotides, arranged in a double helix structure
  • DNA carries genetic information - the genetic code
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2
Q

Is DNA parallel or antiparallel?

A

DNA is antiparallel because the nucleic acid sequences are complementary and parallel, but they go in opposite directions
(the DNA strands are described as being antiparallel because they run in opposite directions)

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3
Q

What does RNA stand for? What is it made up of?

A
  • ribonucleic acid
  • it is made up of only one polynucleotide strand
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4
Q

What is a gene?

A

a gene is a sequence of nucleotides that forms part of a DNA molecule

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5
Q

What is a chromosome?

A

a chromosome is a thread-like structure made up of a DNA molecule that contains all or some of the genetic information of an organism

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6
Q

What is a genome?

A

a genome is the complete set of genes present in a cell

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7
Q

What is the genetic code?

A

DNA contains the genetic code which dictates all the inherited characteristics of an organism
DNA does this by controlling the manufacture of proteins

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8
Q

How are hydrogen bonds formed?

A

hydrogen bonds form when a negative part of a molecule comes into contact with the positively charged hydrogen atom on the same or a different molecule

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9
Q

What groups make up the structure of a nucleotide?

A
  • phosphate group
  • pentose sugar (deoxyribose in DNA, ribose in RNA)
  • nitrogenous base
    (check photo online)
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10
Q

What is the pentose sugar in DNA and RNA? And what are the bases found in RNA and DNA?

A

DNA
- contains the pentose sugar deoxyribose
- bases = adenine, guanine, thymine and cytosine
RNA
- contains the pentose sugar ribose
- bases - adenine, guanine, cytosine and uracil

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11
Q

Describe the basic structure of a DNA molecule?

A
  • DNA molecules are polymers and are made up of many smaller molecules, called nucleotides
  • each nucleotide contains a phosphate group, a pentose sugar molecule, and a nitrogenous base.
  • DNA molecules consist of two DNA strands (polynucleotides), which are twisted around in a spiral shape aka the double helix
  • DNA is held together by hydrogen bonds (between bases) and sugar phosphate backbone
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12
Q

Where is DNA found?

A
  • DNA is found in the nucleus of a cell if it possesses one
  • if the cell does not have a nucleus (i.e. a bacterial cell) its found in the cytoplasm
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13
Q

What are purines and what are pyrimidines? Give examples

A
  • purines are 2-ring structures e.g. adenine and guanine
  • pyrimidines have a single ring structure e.g. ‘CUT’ cytosine, uracil and thymine
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14
Q

Why do the bases in DNA only ever pair in a certain way?

A
  • bases A and G are purines (have two ring structures) whereas C and T are pyrimidines (have single ring structures)
  • the bases pair so that each ‘rung’ of the DNA molecule have three rings
  • this makes the molecule a uniform width along its whole length
  • the bases A and T and the bases C and G are referred to as complementary base pairing?
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15
Q

What dictates how many hydrogen bonds are between each base?

A
  • The shape and chemical structure of the bases dictates how many hydrogen bonds each one can form
  • A and T have two hydrogen bonds
  • C and G have three hydrogen bonds
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16
Q

What is the bond between nucleotides? Where does this bond happen? What type of reaction is this? And what molecule does this form?

A
  • the bond formed between nucleotides is called a phosphodiester bond
  • the bond is between the pentose sugar (carbon 3) and the phosphate group
  • this is a condensation reaction
  • the molecule that forms is called a dinucleotide (if there is a long chain its a polynucleotide)
17
Q

What is a pentose sugar?

A

sugars with 5 carbon atoms are called pentose sugars

18
Q

What is one nucleotide called and what are many nucleotides called?

A
  • one nucleotide is called a mononucleotide
  • lots of nucleotides (a chain of them) is called a polynucleotide
19
Q

How can the phosphodiester bond be broken? And why?

A

The phosphodiester bond can be broken by hydrolysis. This is because the bond is a condensation reaction and releases water so by adding water aka through hydrolysis, the bond is broken

20
Q

What are the difference and similarities between the structures of DNA and RNA?

A
  • an RNA molecule is a single stranded polynucleotide made or ribonucleic acid (RNA) where as DNA has two polynucleotides
  • RNA nucleotide and DNA nucleotide both contain a phosphate group, sugar and base
  • RNA contains ribose sugar whereas DNA contains deoxyribose sugar
  • In RNA the base uracil replaces thymine, RNA never contains thymine whereas DNA does
21
Q

Analysis of a quantity of DNA revealed 54% to be composed of A-T bases. What proportion of the DNA is cytosine?

A

46% of the DNA is C-G base pairs so therefore 23% is cytosine

22
Q

What is protein synthesis? What are the two stages of protein synthesis?

A

-protein synthesis is the process in which polypeptide chains (proteins) are synthesised from DNA in the ribosomes
- 1st stage is transcription and 2nd stage is translation

23
Q

What are the stages in transcription?

A
  1. DNA is held together by hydrogen bonds and sugar phosphate backbone
  2. DNA helicase breaks the hydrogen bonds between the DNA, this unravels it
  3. Free RNA nucleotides start complimentary pairing to the template strand. Adenine pairs with uracil
  4. RNA polymerase now joins the free nucleotides together by phosphodiester bonds and creates mRNA (one polynucleotide strand)
  5. Then mRNA leaves the nucleus to go to the cytoplasm
  6. The DNA now quickly zips back up (to avoid mutations)
24
Q

What are the stages of translation?

A
  1. The mRNA leaves the nucleus to go to the cytoplasm via a nuclear pore
  2. The mRNA attaches to a ribosome at the start codon
  3. The tRNA with an anticodon complementary to the start codon arrives at the ribosome. This tRNA molecule has a specific amino acid attached to it.
  4. Another tRNA molecule binds to the second codon on the mRNA. This brings with it another amino acid.
  5. A peptide bond forms between the two amino acids
  6. The first tRNA molecule then leaves, and the process continues until a stop codon is released
25
Q

Where does transcription take place? Summarise what happens? What does transcription make?

A
  • transcription takes place in the nucleus
  • this is where one of the genes on the entire DNA molecule is copied
  • this copy is made from ribonucleic acid (RNA)
  • this RNA molecule is known as mRNA and can leave the nucleus, carrying the information to the cytoplasm where it is used in the manufacture of proteins (in ribosomes)
26
Q

Where does translation take place? Summarise what happens? What does translation make?

A
  • translation happens on ribosomes in the cytoplasm
  • the process of translation means turning the sequence of bases in the genetic code into the correct sequence of amino acids
  • these amino acids then join together to make a protein
27
Q

What is the RNA that is made during transcription? Why is it known as this?

A
  • the RNA made in the nucleus during transcription is known as messenger RNA (mRNA)
  • because it carries the code from the DNA to the cytoplasm where it is used in the manufacture of proteins
28
Q

Why is mRNA made?

A
  • mRNA is made because DNA cannot pass through the membranes surrounding the nucleus into the cytoplasm so a copy of it is made.
  • mRNA can leave the nucleus vie a nuclear pore
29
Q

What is the template strand?

A
  • the template strand is the strand which the newly made RNA molecule pairs to on the DNA to create a copy of the coding strand
30
Q

What is a coding strand?

A
  • the coding strand is the strand that the newly made RNA makes a copy of
  • (the coding strand was originally paired with the template strand in the DNA before the DNA helicase attached itself to the DNA and split them)
31
Q

What is a codon? What does each codon encode?

A
  • a codon is a sequence of 3 nucleotides (3 bases) that codes for one specific amino acid in proteins
32
Q

What are anticodons?

A
  • anticodons are sequences of trinucleotides that are complementary to codons
  • they are found in tRNA
33
Q

What are mutations?

A
  • mutations are changes in the sequence of bases in DNA
34
Q

What is a substitution mutation?

A

a substitution is a mutation that exchanges one base for another
(i.e. a change in a single ‘chemical letter’ such as switching an A to a G)

35
Q

What is an insertion mutation?

A
  • an insertion mutation is a mutation involving the addition of genetic material
  • it can be small involving a single extra DNA base pair, or large, involving a piece of chromosome
36
Q

What is a deletion mutation?

A
  • a deletion mutation is a mutation that involves the loss of one or more nucleotides from a segment of DNA
  • a deletion mutation can occur during DNA replication, when the enzyme that synthesizes new DNA skips or misses a nucleotide on the template strand
37
Q

Describe the properties of the genetic code?

A
  • because there are 20 amino acids, the code carried by the DNA is a three-base or triplet code
  • each adjacent group of three bases codes for an amino acid
  • the code is non-overlapping aka each code is adjacent
  • one triplet sequence is a start code and 3 are stop codes (called chain terminators)
38
Q

What is meant when a genetic code is described as degenerate?

A
  • there are 64 possible three-letter combinations if the four DNA bases are grouped in triplets
  • this leaves on average three different triplet codes for each of the 20 amino acids
  • because several triplets can code for the same amino acid the code is described as degenerate

Topic 2: Genes and Health (8 decks)

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