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Wize University Biology Textbook > DNA Replication & Repair

DNA Structure and Sequence

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Review of DNA Structure

DNA encodes our genetic information which eventually gives rise to RNA and proteins. Important features of DNA are:
  • Double helix.
  • Composed of a sugar-phosphate backbone and nucleotide bases.
  • Complementary strands are anti-parallel to one another.
  • Runs from 5’→3’
  • Nucleotide bases are connected by hydrogen bonds.
  • Adenine (A) with Thymine (T)
  • Guanine (G) with Cytosine (C)
  • Purines hydrogen bond with pyrimidines:
  • Purines = A & G
  • Pyrimidines = T & C
  • In RNA, Uracyl (U) replaces T
  • C and G have 3 hydrogen bonds between one another, while A and T have only two.
  • This makes the bonds between C and G harder to break, requiring more energy (i.e. higher temperature).

Wize Tip

Remember the mnemonic below to memorize which nucleotides are purines and which are pyrimidines:

  1. CUT the Py = Cytosine, Uracil and Thymine are Pyrimidines.
  2. Pure As Gold = Purines are adenine and Guanine.




Photo by OpenStax / CC BY



PAGE BREAK

How is the DNA backbone elongated?

  • Phosphodiester bonds form between the 3' -OH group of one nucleoside to the 5' phosphate group of an incoming nucleoside.
Photo by Mykhal / CC BY

Practice: Levels of DNA Structure

Select the three levels of DNA structure.



Practice: Nucleotide Base Pairing

Which of the following is the correct 5' to 3' sequence of the complimentary strand to: 5'-AGGTCTGATTCGTA-3' ?
Extra Practice
What is the base sequence of the DNA strand that would be complimentary to the following strand of DNA – 3’ TAGCTACGTTAT 5’?
The genome of the bacterium Mycobacterium tuberculosis contains 65.6% GC base pairs. What percentage of the genome is made up of purines?
A nucleic acid was analyzed and found to contain 32% A, 18% G, 17% C, and 33% T. The nucleic acid must be:
i. Single-stranded
ii. Double-stranded
Practice: Denaturation
You are analyzing two separate DNA sequences that are approximately equal in length. You find that Sequence 1 has a G-C content of 45%. Sequence 2 has a G-C content of 52%. Which DNA sequence do you expect to have a higher denaturation temperature? Why?
The percent of cytosine in a double-stranded DNA is 21. What is the percent of thymine in that DNA?
What is the base sequence of the DNA strand that would be complimentary to the following single-stranded DNA molecule? Write it in the 5’ to 3’ direction.
5'-GGATCTGCTATG-3'
Consider the 5' and 3' designations:
i. They must be on the same ends for two DNA strands in a helix (parallel)
ii. They must be on opposite ends for two DNA strands in a helix (antiparallel)
The genome of the bacterium Mycobacterium tuberculosis contains 65.6% GC base pairs. What percentage of the genome is made up of purines?
The percent of cytosine in a single-stranded DNA is 21. What is the percent of thymine in that DNA?
For double stranded DNA, consider the following ratios:
I. A/G
II. C/T
A nucleic acid was analyzed and found to contain 32% A, 18% G, 17% C, and 33% T. The nucleic acid must be:
i. Single-stranded
ii. Double-stranded
You collect a double stranded DNA sample that happens to be 30% adenine. What percent will be cytosine?
Practice: 32P Culture
You are growing a cell culture in radioactive Phosphorus (32P) what molecules will be radioactive?
Select all that apply, answer may or may not involve multiple chapters.
This type of bond holds together complementary strand of DNA. Answer is one word
Nucleotides are joined together to form long chains though a ___ reaction to form a ____ bond
Practice: Meiosis (Telomeres)
A hedgehog has a diploid number of 48 chromosomes. How many telomeres would you find in a a hegdehog gamete at the beginning of telophase II?
Practice: DNA
The two strands of the DNA helix are held together by _____ bonds while the sugar-phosphate backbone is linked by _______ bonds.
The 5' end of the DNA helix ends with ______ while the 3' end of the helix ends with ______.
Transcription
Label the following statements as true or false
A. When RNA polymerase transcribes DNA in to RNA, the RNA is an exact copy of the DNA stand being transcribed.
B. Uracil complements with adenine in RNA.
DNA structure
Label the following statements as True or False
A. The 3' end of a DNA strand ends in an OH group
B. If the percentage of pyrimidines in a DNA strand is 40% then purines will occur at 60%
You are growing a population of bacteria in normal bacterial culture. You then decide to introduce adenines into the cells that are covalently bonded to a fluorescent tag. After 2 rounds of replication in these cells, where would you find the fluorescent signal?
Which of the following is not a component of RNA?
Which of the following stabilizes the DNA helix?
To generate a DNA polymer, where is the bond created?
What DNA base is replaced by uracil in RNA?
Which of the following is false regarding DNA?
Which of the following is incorrect regarding DNA?
What DNA nucleotide does uracil replace in RNA?
What nucleotide pairs with cytosine in a DNA helix?
What makes up the backbone of a DNA strand?
Which of the following is incorrect regarding DNA?
Practice: Denaturation
You are analyzing two separate DNA sequences that are approximately equal in length. You find that Sequence 1 has a G-C content of 45%. Sequence 2 has a G-C content of 52%. Which DNA sequence do you expect to have a higher denaturation temperature? Why?
You are analyzing the genome of a certain organism and find that it is made up of 34% thymine bases. Therefore, you reason there must be
16
% guanine bases.
Nucleic Acid -BIOl200
You are analyzing a double stranded DNA sequence that is 80 base pairs long. The DNA has 45 thymine (T) bases. How many cytosine (C) bases are present in this DNA structure?
Use the codon dictionary below to complete the following table. Assume that reading is from left to right and that the columns represent transcriptional and translational alignments.
What is the base sequence of the DNA strand that would be complimentary to the following strand of DNA – 3’ TAGCTACGTTAT 5’?
The percent of cytosine in a double-stranded DNA is 21. What is the percent of thymine in that DNA?
Which pairings of nitrogenous bases are correct?
i. Adenine and uracil
ii. Adenine and guanine
Practice: Nucleic Acid
A nucleic acid was analyzed and found to contain 32% A, 18% G, 17% C, and 33% T. The nucleic acid must be:
i. Single-stranded
ii. Double-stranded
Practice: Nitrogenous Bases
Which pairings of nitrogenous bases are wrong?
i. Adenine and uracil
ii. Adenine and guanine
Practice: Complimentary Strand
What is the base sequence of the DNA strand that would be complimentary to the following single-stranded DNA molecule? Write it in the 5’ to 3’ direction.
5'-TCATTGCGGA-3'
Strands that make up DNA are antiparallel, this means:
DNA replication in S phase can be observed using nucleotides that have been tagged with a radioactive or fluorescent label. Why would you need to be careful when choosing which nucleotide to label?
Write a point form essay outline for the following prompt:
The central dogma of molecular biology is that DNA is transcribed to RNA, which is translated into protein. As such, when we think of DNA, we often picture transcriptionally active euchromatin. However, approx. 10% of interphase DNA in eukaryotes is organized as transcriptionally inactive heterochromatin. Explain the importance of heterochromatin.
Thesis statement: