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Dna. Flashcards

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1
Q

DNA Is

A

A stable information carrying molecule, that stores genetic code (Deoxyribonucleic acid)

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2
Q

Genetic code is

A

The information which instructs a cell which proteins to make

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3
Q

DNA is a polymer of

A

Monomer subunits called nucleotides

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4
Q

Nucleotides contain what atoms

A

C, H, O, N, and P

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5
Q

What are the three parts of nucleotides

A

-Phosphate group
-Deoxyribose sugar
-Nitrogenous base
(All joined by covalent bonds)

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6
Q

How is single-strand DNA formed

A

When nucleotides join together in a chain by covalent bonds which form between the phosphate group of one nucleotide and the deoxyribose of the other, forming a sugar-phosphate backbone.

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7
Q

How is a double-stranded DNA formed

A

when 2 single strands of DNA twist around each other to form a double helix which is held together by hydrogen bonds between the nitrogenous bases of nucleotides on different strands

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8
Q

Are the 2 strands parallel

A

They are anti parallel (run parallel to each other but in opposite directions)

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9
Q

What are the 4 nitrogenous bases in DNA

A

Adenine, Cytosine, Guanine, and Thymine

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10
Q

What structural groups do these nitrogenous bases belong to

A

Adenine and guanine are purines (2 rings containing nitrogen), Cytosine and thymine are pyrimidines (1 ring containing nitrogen)

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11
Q

What are the complimentary pairs and why

A

A and T (both form 2 hydrogen bonds)
C and G ( both form 5 hydrogen bonds)

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12
Q

Describe how the structure of DNA is related to its functions

A

-The sugar phosphate backbone provides strength and stability to protect the bases and hydrogen bonds.
-It’s a long molecule and its coiled and compact so it can store lots of information.
-It’s base sequence allows information to be stored.
-Double stranded so replication can occur.
-complimentary base pairing so accurate identical copies can be made.
-Hydrogen bonds are weak so can easily be broken for replication.
-Many hydrogen bonds are strong.

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13
Q

Compare the roles of RNA and DNA

A

DNA stores genetic material whereas RNA transfers genetic information from DNA in the nucleus to ribosomes in the cytoplasm, where proteins are made.

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14
Q

Compare the structures of DNA and RNA

A

-RNA is single stranded, DNA is double stranded
-RNA is shorter and less stable
-RNA is made up of nucleotides containing the nitrogenous bases adenine, cytosine, guanine, and uracil.
-Pentase sugar in RNA is ribose.

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15
Q

Compare the roles, structure, and diagram of mRNA and tRNA

A

Role:
-mRNA carries specific nucleotide bases to ribosomes.
-tRNA carries specific amino acids to ribosomes.

Structure:
-mRNA is single stranded and its codons (every 3 bases) bind to complimentary tRNA on anticodons.
-tRNA is single stranded (clover leaf), These strands pair on the same strand, its anticodon binds to a complimentary codon on mRNA.

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16
Q

Describe the steps of DNA replication

A

DNA helical enzyme unwinds the DNA double helix by breaking the H bonds which hold the strands together.

Bases on each DNA are exposed.

Each strand acts as a template. Free nucleotides attach to the exposed bass on each strand: A to T and C to G (complimentary base pairing)

DNA polymerase enzyme joins ides with phosphodiester bonds to form new strands.

H bonds form between the bases of the old and new strands.

Two new daughter DNA helices are made, each one an exact replica of the original (parent) helix.

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17
Q

Explain why DNA replication is semi-conservative

A

One old parent helix is replaced by two identical daughter helixes.

Each daughter helix contains one old DNA strand and one new DNA strands meaning both parent single strands have been conserved.

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18
Q

What is a gene

A

A sequence of DNA nucleotide bases that code for a polypeptide

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19
Q

What is a genome

A

A complete set of genes in a cell

20
Q

What is locus

A

The specific location of a gene

21
Q

What is allele

A

An alternative version of the same gene

22
Q

What is a proteome

A

The full range of proteins a cells produces

23
Q

What are the multiple repeats

A

Short base sequences repeated over again

24
Q

Describe the triplet code

A

Non overlapping, always read in one direction, universal.

25
Q

Although there are 64 triplet combinations there are only 20 amino acids, why is this?

A
  1. Because the code is degenerate, some triplets code for the same amino acid.
  2. Some triplets code for instructions to start or stop making a polypeptide rather than an amino acid.
26
Q

A polypeptide will have fewer amino acids than its gene has triplet codes, why?

A
  1. Genes contain coding regions called exons and non coding sections called introns.
  2. Some triplets code for instructions.
27
Q

Where does transcription take place?

A

In the nucleus

28
Q

Describe transcription

A

During transcription part of the DNA double helix unzips when hydrogen bonds which hold 2 strands of DNA together are broken and RNA polymerase makes a complimentary mRNA copy of the DNA template strand. It forms phosphodiester bonds between 3 RNA nucleotides joining them together to make an mRNA strand.

C is copied as G on mRNA, G is copied as C on mRNA.

T is copied as A on mRNA, but A is copied as Uracil.

29
Q

Where does splicing take place

A

In the nucleus

30
Q

Describe splicing

A

Transcription makes pre mRNA this is an exact copy of the gene on the DNA as it contains exons and introns, these introns are cut out of the pre mRNA and the exons are joined together which results in a mature mRNA containing only exons.

31
Q

Where does translation take place

A

Cytoplasm,

32
Q

Describe translation

A

mRNA made in the nucleus during transcription carries a copy of the DNA and after splicing, it leaves the nucleus through holes in the nuclear envelope called nuclear pores. The mRNA is then translated by ribosomes in the cytoplasm, mRNA attaches to a ribosome and each mRNA codon binds temporarily to a complimentary anticodon on tRNA by hydrogen bonds. Each tRNA molecule carries a specific amino acid, and ribosomes join to the amino acids that are carried by a ten tRNA/s by forming peptide bonds between them. When hundreds of amino acids are joined together this way, a polypeptide chain is formed.

The sequence of mRNA bases determines the sequence of amino acids in a polypeptide (its primary structure) this in turn determines the 3D tertiary structure of a protein, therefore its shape and function.

33
Q

What is a gene mutation

A

Random changes in dna base sequence

34
Q

When do gene mutations occur

A

They occur as spontaneous errors during dna replication and this is how alternative versions of genes (alleles) are created

35
Q

Name some mutagenic agents

A

X rays and Mustard gas

36
Q

What are the 4 types of DNA mutation

A

Substitution, deletion, insertion, duplication

37
Q

Describe substitution

A

Where 1 nucleotide base pair is replaced by another

38
Q

Describe deletion

A

Where 1 nucleotide base pair is removed from a gene

39
Q

Describe insertion

A

Hertz 2 nucleotide base pair is added to a gene

40
Q

Describe duplication

A

Where a region of nucleotides are repeated in a gene

41
Q

Describe inversion and translocation

A

Inversion is when one or more bases are reversed, translocation is when a sequence of bases is moved from one location to another

42
Q

Gene mutation may change what

A

The sequence of codons.
The amino acid sequence of a polypeptide.
The position of H, ionic and disulphide bonds which hold together a proteins tertiary structure.
The 3D shape and function of a protein.
The protein may not be able to function properly or at all.

43
Q

Why do we say may change

A
  1. Deletions and insertions are more likely to produce a non functional protein than subsitutions because removal of one base pair changes every triplet code after the point of deletion making a completely different protein this is called a frame shift mutation.
  2. Substitutions are more likely to produce a non functional protein is degenerate and even if one amino acid is changed it may not alter the proteins structure.
44
Q

siRNA is

A

Small interfering RNA which is a special type of rna that is about 20 pairs long and is double stranded, siRNA prevents translation of other mRNA molecules by end interference.

45
Q

Describe RNA interference

A
  1. the cytoplasm siNA binds to a protein called “RISC” to form a complex.
    2.The RISC protein breaks the double-stranded siRNA into its separate strands. One
    strand remains attached to the protein, while the other strand is discarded.
  2. The remaining siRNA strand binds to a specific mRNA molecules in the cytoplasm
    that have a complementary sequence (by complementary base pairing, C to G, A to
    U). Therefore one type of siRNA binds only to one sort of mRNA.
  3. This binding causes the RISC protein to cut (cleave) the mRNA molecule in two.
  4. Enzymes finish off the job by cutting the mRNA into pieces by so it can’t be translated
46
Q

SiRNA can be used to what

A

Silence genes, A 20-base pair siRNA molecule can be synthesised in the
laboratory with a sequence that is complementary to part of the gene that is to be silenced.
The siRNA created is specific - it will only prevent translation of mRNA transcribed from a
specific gene.

47
Q

Applications of siRNA include

A
  1. Genetically-modifying crop plants by silencing undesirable genes e.g. in the Flavr
    Savr tomato a gene causing ripening was silenced causing the tomatoes to stay fresh
    for longer.
  2. Treating cancer in human patients by preventing translation of oncogenes to stop
    them from making proteins that lead to uncontrolled cell division.
  3. Treating genetic disease by preventing translation of genes that code for harmful
    proteins.
  4. Antiviral therapies e.g. silencing the gene for the receptor protein used by HIV to
    enter cells, so that the cell cannot make the receptor. therefore HIV cannot infect
    cells.

Human Biology (12 decks)

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