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

Mod 1- DNA & Gene Structure Flashcards

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.

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
What are the two main components of a gene?
**Genes are discontinuous so are split into:** Exons and introns ## Footnote Exons contain information to make a protein; introns contain information not needed for protein synthesis
26
What is the average number of introns and exons in a human gene?
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
What is gene expression?
The process by which the information in a gene is read ## Footnote This leads to the production of proteins and RNAs
28
What are the functional end products of gene expression?
Proteins Proteins play many roles in the cell; noncoding RNAs also play important roles
29
What distinguishes unique genes from gene families?
Unique genes have one copy other genes occur in families = related or same gene ## Footnote Gene families can be simple or complex
30
What are simple multi-gene families?
Families where all genes are the same They are identical and produce the same product (amplify) ## Footnote Example: ribosomal RNA genes
31
What are complex multigene families?
- 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
How do multigene families arise?
Through gene duplication (during meiosis) After duplication, sequences gradually change so the members of the gene family have slightly different sequences
33
What is the molecular clock?
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
What are pseudogenes?
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
Fill in the blank: The human globin genes are located on chromosome ___ and chromosome ___.
16- Alpha- globin genes 11- beta-globin genes
36
Why is DNA important?
- 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
Where does a phosphodiester bond form?
Bonds to oxygen
38
What is the typical process of gene expression?
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
What are some examples of non-coding RNA?
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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