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Molecular Biology > Mod 1- DNA & Gene Structure > Flashcards

Mod 1- DNA & Gene Structure Flashcards

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1
Q

What is the composition of DNA?

A

DNA is a polymer of nucleotides.

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2
Q

Who discovered the double helix structure of DNA?

A

James Watson and Francis Crick in 1953.

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3
Q

What are the two roles of genes in the cell?

A
  • Units of biological information
  • Units of inheritance
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4
Q

What are the three parts of a nucleotide?

A
  • Sugar = 2’-deoxyribose (2 prime is the position in the sugar)
  • Phosphate groups
  • Base = nitrogenous
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5
Q

What are the four bases found in DNA?

A

Attached to sugar with a β-N-glycosidic bond (base attached to sugar)

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T)

A & G are purines
C & T are pyrimidines

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6
Q

What is Chargaff’s Rule?

A

The total number of purines (A & G) in a DNA molecule is equal to the total number of pyrimidines (C & T)

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7
Q

What is the directionality of DNA strands?

A

DNA has a direction, e.g., 5’ to 3’.

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8
Q

What type of structure does DNA have in living cells?

A

DNA is a double helix made up of two polynucleotide strands.

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9
Q

What is the significance of the DNA double helix being antiparallel?

A

The two strands run in opposite directions.

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10
Q

What bonds hold the two strands of DNA together?

A

Hydrogen bonds.

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11
Q

What is complementary base-pairing in DNA?

A

A pairs with T and G pairs with C.

This stabilises the DNA but allows for separation

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12
Q

What is GC content?

A

The amount of G + C nucleotides in an organism’s DNA.

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13
Q

What is the GC content of human DNA?

A

40.3%.

This is never 50/50 with A-T content

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14
Q

What are the three types of DNA double helix?

A

B-DNA = normal/ most common form of DNA = right-handed

A-DNA = most rare DNA (‘messy’) = right-handed

Z-DNA = found in our DNA in small amounts = left-handed

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15
Q

What is the most common form of DNA?

A

B-DNA.

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16
Q

Under what conditions does A-DNA form?

A

When there is not enough water around – dehydrating conditions.

17
Q

What is known about the biological activity of Z-DNA?

A

Found naturally with B-DNA only in certain regions but its function is still not clear.

Associated with some diseases

18
Q

Fill in the blank: DNA is vital for all _______.

A

[living things]

19
Q

True or False: The double helix structure of DNA was solely based on Watson and Crick’s work.

A

False.

20
Q

What are the names of the four nucleotides in DNA?

A
  • 2’-deoxyadenosine 5’-triphosphate (dATP)
  • 2’-deoxyguanosine 5’-triphosphate (dGTP)
  • 2’-deoxycytidine 5’-triphosphate (dCTP)
  • 2’-deoxythymidine 5’-triphosphate (dTTP)
21
Q

What is a gene?

A

A segment of a DNA molecule containing biological information

(A very small portion of the genome)

Genes are the functional units of the genome

22
Q

How is the length of a DNA molecule measured?

A

In base pairs (bp)

1000 bp = 1 kilobase (kb),
1000 kb = 1 megabase (Mb)

23
Q

What is the length range of genes?

A

Shortest genes: about 100 bp (eg tRNAs)

Longest genes: about 2,400,000 bp (eg.human muscle protein dystrophin)

24
Q

Do the longest genes contain 24,000 times more biological information than the shortest genes?

A

No

This is a misconception

25
Q

What are the two main components of a gene?

A

Genes are discontinuous so are split into:

Exons and introns

Exons contain information to make a protein; introns contain information not needed for protein synthesis

26
Q

What is the average number of introns and exons in a human gene?

A

8 introns and 9 exons

Mean intron length is 3365 bp, mean exon length is 145 bp

In many genes, the introns can make up almost 90% of the total length

27
Q

What is gene expression?

A

The process by which the information in a gene is read

This leads to the production of proteins and RNAs

28
Q

What are the functional end products of gene expression?

A

Proteins

Proteins play many roles in the cell; noncoding RNAs also play important roles

29
Q

What distinguishes unique genes from gene families?

A

Unique genes have one copy

other genes occur in families = related or same gene

Gene families can be simple or complex

30
Q

What are simple multi-gene families?

A

Families where all genes are the same

They are identical and produce the same product (amplify)

Example: ribosomal RNA genes

31
Q

What are complex multigene families?

A
  • Families where genes are not identical but have similar DNA sequences
  • Code for similar but non-identical proteins
  • Provides proteins with slightly different functions which allows increased organismal complexity

Example: human globin genes

32
Q

How do multigene families arise?

A

Through gene duplication (during meiosis)

After duplication, sequences gradually change so the members of the gene family have slightly different sequences

33
Q

What is the molecular clock?

A

A measure of the rate at which the sequence of a gene changes

It helps determine when a pair of genes were formed by duplication

If more similar = shorter amount of time

34
Q

What are pseudogenes?

A

Genes that have lost their function and no longer make sense

There are four pseudogenes in the alpha-globin family and one in the beta-globin family

35
Q

Fill in the blank: The human globin genes are located on chromosome ___ and chromosome ___.

A

16- Alpha- globin genes

11- beta-globin genes

36
Q

Why is DNA important?

A
  • it is vital for all living things
  • it holds instructions for an organisms development, survival and reproduction due to its structure
  • long term storage of information = DNA is very stable
37
Q

Where does a phosphodiester bond form?

A

Bonds to oxygen

38
Q

What is the typical process of gene expression?

A

Gene —> RNA —> Protein

Gene to RNA = via transcription by polymerase

RNA is the intermediate = 96% is non-coding RNA, 4% is coding RNA that turns into protein

RNA to Protein = via translation by ribosome

This is the classic pathway BUT sometimes stays as RNA which have different independent functions

39
Q

What are some examples of non-coding RNA?

A

tRNA- adds amino acids to chain
rRNA- makes up part of ribosome
snRNA- involved in splicing
snoRNA- causes brain disorders when mutated

Molecular Biology (10 decks)

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