Click the following link for a DNA Structure and Replication Student Learning Guide

1. Introduction

DNA, 108px-DNA_icon.svgDNA stands for deoxyribonucleic acid. Its function is

  1. To transmit hereditary information from one generation to the next.
  2. To control the cell through determining which proteins (and RNAs — a close relative of DNA) that the cell will produce. This, in turn, determines how a single cell develops into a complex, integrated, multicellular organism.

2. Three Key DNA-related process: Replication, Transcription, and Translation

2a. Replication

replication
DNA replication

The process by which cells copy their DNA is called replication.

binary fission, wikipedia,494px-Collodictyon_telophase_constrict
In order to reproduce, unicellular organisms have to grow, replicate their DNA, and then split into two.

In a unicellular (single-celled) species, DNA replication is one of the key parts of reproduction. To reproduce, a single-celled organism grows bigger, replicates its DNA, then divides itself in two. You can see a unicellular organism (Collodictyon) dividing into two at right.

For multicellular organisms like us, DNA replication is required for growth, repair and reproduction.

03a_cell-cycle-labeled-smv-remixAs we’ve seen in a previous tutorial, DNA replication is a key part of the cell cycle. It occurs during the S phase of interphase.

2b. DNA makes RNA makes protein: Transcription and Translation

DNA controls the cell by specifying which proteins the cell makes.

DNA is information. But on its own, DNA is powerless. By contrast, proteins can do things. As enzymes, protein can take molecules apart or put them together. As muscle, protein can make organisms move.

Here’s how DNA controls the cell through protein:

    1. DNA stays in the nucleus. Through transcription, messages from DNA are sent to the cytoplasm.
    2. These messages are in the form of RNA (a molecule that is closely related to DNA).
    3. Through translation, RNA messages are changed into protein, the action molecule of the cell.
    4. The key sequence is DNA ? transcription? RNA ? translation ? protein.

DNA makes RNA makes protein is a central idea in biology. In fact, it’s known as CENTRAL DOGMA of molecular genetics. Molecular genetics is the field that studies the molecules of inheritance: their structure, function, and behavior.

00_simple transcription, translation, numberedWe’ll spend a lot of time clarifying these processes in later tutorials, but the key ideas are captured in the diagram to the right.

  • The cell membrane is at 1. The nuclear membrane is at 2.
  • DNA (3) gets transcribed (4) into RNA (5).
  • The RNA leaves the nucleus and enters the cytoplasm (6)
  • In the cytoplasm, RNA gets translated into protein (8). As we’ll see, translation happens at ribosomes (7)

DNA makes RNA makes protein is the essential recipe for life. 

3. Where DNA is found

plant_cell_numbered
plant cell (modified from wikimedia commons)

3a. In eukaryotes

In eukaryotic cells, most of the DNA is found in the chromosomes, within the nucleus. In the diagram of a plant cell to your left, the chromosomes are shown at number 8. (Note that this drawing is slightly inaccurate. Most of the time the DNA is spread throughout the nucleus. The “X” shape only appears when the cell is about to divide).

Two eukaryotic organelles, mitochondria (5) and chloroplasts (10), also have DNA. These organelles have DNA because they evolved from once-independent prokaryotic cells that long ago took up residence inside a larger, eukaryotic cell. The DNA in these organelles is similar to the prokaryotic DNA described below.

prokaryotic cell (chromsome, plasmids)
Prokaryotic cell (modified from and upload by LadyofHats, wikimedia commons)

3b. In prokaryotes

Prokaryotic cells lack a nucleus and complex, membrane-bound organelles. This cell type is found, most notably, in bacteria.

In prokaryotes, most of the DNA is found in the cytoplasm, in a single, looped chromosome (looped because the end is connected to the beginning). Some additional DNA is located outside the main chromosome in small loops of DNA called plasmids. Bacterial cells use plasmids to exchange genes with one another. As we’ll see later in the course, plasmids are also essential tools for introducing new genes into bacterial during the process of genetic engineering.

phage3.c. In viruses

Viruses consist of DNA (or RNA) surrounded by protein. There can also be additional layers outside the protein. Viruses attack cells, and use the cell’s machinery to make more viruses.

 

4. Quiz: DNA Concepts

[qwiz style = “border: 3px solid black; ” random = “true” qrecord_id=”sciencemusicvideosMeister1961-DNA Concepts (M13)”]

[h] Quiz: DNA Concepts

[i]

[q labels = “top”]

 

[l]main bacterial chromosome

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]plasmid

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]cytoplasm

[fx] No.  Please try again.

[f*] Great!

[q labels = “top”]

 

[l]RNA

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]translation of RNA to protein

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]DNA

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]cell membrane

[fx] No.  Please try again.

[f*] Excellent!

[l]cytoplasm

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[l]protein

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[l]transcription of DNA to RNA

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]nuclear membrane

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[q labels = “top”]Label the four parts of a  plant cell that have a direct connection to DNA.

 

[l]chromosomes

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]chloroplast

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]mitochondria

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]nuclear membrane

[fx] No.  Please try again.

[f*] Great!

[q]Copying DNA is known as ____________

[c]transcription

[c*]replication

[c]translation

[f]No. You’re looking for the word that’s used when spoken words are changed into written words

[f]Yes! Copying DNA is known as replication.

[f]No. Translation is making protein from RNA.

[q]The process of making RNA from DNA is known as ________

[c*]transcription

[c]replication

[c]translation

[f]Yes. The process of making RNA from DNA is known as transcription.

[f]No. Replication means copying. You’re looking for the word that’s used when you take audio and write down the words.

[f]No. Translation involves taking RNA and making it into protein. You’re looking for the word that’s used when you take audio and write down the words.

[q]The process of making protein based on RNA instructions is known as ________

[c]transcription

[c]replication

[c*]translation

[f]No. Transcription is making RNA from DNA. You’re looking for the word that’s used when someone changes the words in one language into another language.

[f]No. Replication means copying.You’re looking for the word that’s used when someone changes the words in one language into another language.

[f]Yes. Translation involves taking RNA and making it into protein.

[q]In the diagram below, DNA is shown at

[textentry single_char=”true”]

[c*]3

[f]Yes. In the diagram above, DNA is shown at 3.

[c]*

[f]No. Look for the double helix.

[q]In the diagram below, RNA inside the nucleus is shown at

[textentry single_char=”true”]

[c*]5

[f]Yes. In the diagram above, RNA inside the nucleus is shown at 5.

[c]*

[f]No. Look for a single helix (corkscrew shape) inside the nucleus.

[q]In the diagram below, newly made protein is shown at

[textentry single_char=”true”]

[c*]8

[f]Yes. In the diagram above, newly made protein is shown at 8.

[c]*

[f]No. Look something being made by the ribosome (shown at 7)

[q]In the diagram below, a ribosome is shown at

[textentry single_char=”true”]

[c*]7

[f]Yes. In the diagram above, a ribosome is shown at 7

[c]*

[f]No. Look for something that’s reading RNA, making protein.

[!]card 1++++++++++++[/!]

[q]The central dogma of molecular genetics is ________ makes RNA, makes protein.

[hangman]

[c]DNA

[f]The central dogma of molecular genetics is DNA makes RNA, makes protein.

[!]card 2++++++++++++[/!]

[q]DNA stands for ___________ acid

[hangman]

[c]deoxyribonucleic

[f]DNA stands for deoxyribonucleic acid.

[!]card 4++++++++++++[/!]

[q]The copying of DNA is called ________

[hangman]

[c]replication

[f]The copying of DNA is called replication.

[!]card 5++++++++++++[/!]

[q]The central dogma of molecular genetics is DNA makes RNA makes ____________.

[hangman]

[c]protein

[f]The central dogma of molecular genetics is DNA makes RNA makes protein.

[!]card 6++++++++++++[/!]

[q]In a eukaryotic cell, DNA always stays in the __________________.

[hangman]

[c]nucleus

[f]Yes! In a eukaryotic cell, DNA always stays in the nucleus.

 

[!]card 8++++++++++++[/!]

[q]The word for the transfer of DNA information into RNA is ________________.

[hangman]

[c]transcription

[f]The word for the transfer of DNA information into RNA is transcription.

[!]card 9++++++++++++[/!]

[q]The word for the transfer of RNA information into protein is ________________.

[hangman]

[c]translation

[f]Nice! The word for the transfer of RNA information into protein is translation.

[!]card 10++++++++++++[/!]

[q]The “action molecule” of the cell is ___________________.

[hangman]

[c]protein

[f]Correct. The “action molecule” of the cell is protein.

[!]card 11++++++++++++[/!]

[q]The molecule which brings DNA information to the cytoplasm is _______

[hangman]

[c]RNA

[f]Good job! The molecule which brings DNA information to the cytoplasm is RNA.

[!]card 13++++++++++++[/!]

[q]In a eukaryotic cell, the DNA is organized into multiple ______________.

[hangman]

[c]chromosomes

[f]Yes. In a eukaryotic cell, the DNA is organized into multiple chromosomes.

 

 

[!]card 16++++++++++++[/!]

[!]card 17++++++++++++[/!]

[!]card 18++++++++++++[/!]

 

[!]card 20++++++++++++[/!]

[q]A cellular parasite which can have DNA or RNA as its genetic material is a ______________

[hangman]

[c]virus

[f]Yes. A cellular parasite which can have DNA or RNA as its genetic material is a virus

[!]card 21++++++++++++[/!]

[q]A tiny circle of DNA found outside the main bacterial chromosome is a _____________

[hangman]

[c]plasmid

[a]Nice job. A tiny circle of DNA found outside the main bacterial chromosome is a plasmid

[!]card 22++++++++++++[/!]

 

[!]card 23++++++++++++[/!]

[!] Question 1+++++++++++++[/!]

[q]Of the choices below, which is the only animal cell organelle that contains its own DNA?

[c]2      [c]3      [c]6      [c*]7      [c]8      [c]9

[f]No. Number 2 is pointing to the cell membrane. There’s no DNA there.

[f]No. Number 3 is pointing to the golgi apparatus. There’s no DNA there.

[f]No. Number 6 is pointing to the ribosomes. They’re made of RNA, not DNA.

[f]Yes. Number 7 is pointing a mitochondrion. Mitochondria evolved from free living prokaryotic bacterial cells, and have their own DNA.

[f]No. Number 8 is pointing to the centrioles. There’s no DNA there.

[f]No. Number 9 is pointing to the Endoplasmic Reticulum. There’s no DNA there.

[!] Question 3++++++++++++++[/!]

[q]In a plant cell, which of the following organelles DOES NOT have DNA.

[c]mitochondrion

[c]chloroplast

[c]nucleus

[c*]golgi apparatus

[f]No. The mitochondrion, which is an evolutionary descendant of an independent prokaryotic cell, contains its own DNA.

[f]No. The chloroplast, which is an evolutionary descendant of an independent, photosynthetic prokaryotic cell, contains its own DNA.

[f]No. The nucleus is the main storehouse of the cell’s DNA.

[f]Yes. The Golgi apparatus is one of many cell organelles that does NOT contain its own DNA.

[!] Question 5++++++++++++++[/!]

[q]In a eukaryotic cell, chromosomes are located in the

[c]Cell membrane

[c*]nucleus

[c]endoplasmic reticulum

[c]ribosomes

[f]No. In a eukaryotic cell, chromosomes are located in a membrane-bound organelle in the center of the cell. What would that be?

[f]Yes. In a eukaryotic cell, chromosomes are located in the nucleus.

[f]No. In aeukaryotic cell, chromosomes are located in a membrane-bound organelle in the center of the cell. What would that be?

[f]No. In a eukaryotic cell, chromosomes are located in a membrane-bound organelle in the center of the cell. What would that be?

[!] Question 6++++++++++++++[/!]

[q]The diagram below represents

[c*]replication

[c]transcription

[c]translation

[f]Yes. Replication is the copying of new DNA from parent DNA.
[f]No. Transcription is the transfer of DNA information into RNA.
[f]No. Translation is the transfer of RNA information into protein.

[!] Question 9++++++++++++++[/!]

[q]Tiny circles of DNA outside the main bacterial chromosome are called

[c]replicons

[c*]plasmids

[c]chromatelles

[f]No. “Replicons” makes sense, but it’s a made up term (sorry!). Here’s a hint: these little circles of DNA are found in the cell’s cytoPLASM.

[f]Yes. These little circles of extra-chromosomal DNA are known as plasmids.

[f]No. “Chromatelles” is a made up term (sorry!). Here’s a hint: these little circles of DNA are found in the cell’s cytoPLASM.

[!] Question 10++++++++++++++[/!]

[q]In the diagram below, translation is represented by which number?


[c]1   [c]2   [c]3  [c]4     [c]5     [c]6     [c*]7

[f]No. 1 represents the cell membrane. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]No. 2 represents the nuclear membrane. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]No. 3 represents DNA. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]No. 4 represents transcription. During transcription, DNA information is transferred to RNA. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]No (but you’re close). 5 represents RNA. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]No. 6 represents the cytoplasm. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[f]Yes. 7 represents translation, or protein synthesis. Translation is when instructions in RNA are converted into protein. Which number could represent this process?

[!] Question 11++++++++++++++[/!]

[q]Which number is pointing to the main bacterial chromosome?

[c]1

[c]2

[c*]3

[f]No. 1 is pointing to a plasmid.
[f]No. 2 is pointing to the cytoplasm.
[f]Yes. 3 is pointing to the main bacterial chromosome.

[!] Question 12++++++++++++++[/!]

[q]Your genes are made of

[c]protein

[c*]DNA

[c]RNA

[f]No. Your genes code for protein, but they’re not made of DNA.

[f]Yes.  Your genes are made of DNA.

[f]No. RNA is a messenger of genetic information. What is the molecule that has the genetic information that you inherit.

[!] Question 13++++++++++++++[/!]

[q]The phrase “DNA makes RNA makes protein” is also known as molecular genetics’

[c]core concept

[c]key idea

[c*]central dogma

[f]No. “DNA makes RNA makes protein” is a core concept in molecular genetics, but this concept is so important that it has a special name.

[f]No. “DNA makes RNA makes protein” is a key idea in molecular genetics, but this concept is so important that it has a special name.

[f]Yes. “DNA makes RNA makes protein” is the central dogma of molecular genetics.

[!] Question 15++++++++++++++[/!]

[q]Which number is pointing to a plasmid?

[c*]1

[c]2

[c]3

[f]Yes. 1 is pointing to a plasmid. Plasmids are small loops of DNA outside the main chromosome.
[f]No. 2 is pointing to the cytoplasm.
[f]No. 3 is pointing to the main bacterial chromosome.

[!] Question 16++++++++++++++[/!]

[q] _______ always stays in the nucleus. It controls the cell by sending out messages in the form of _______

[c]RNA….protein

[c]DNA…protein

[c]RNA…DNA

[c*]DNA…RNA

[f]No. RNA is transcribed in the nucleus and then moves to the cytoplasm.

[f]No. You’re right about DNA, but there’s another molecule that brings DNA’s messages out to the cytoplasm.

[f]No. You’ve got the two reversed.

[f]Yes! DNA always stays in the nucleus. It controls the cell by sending out messages in the form of RNA.

[!] Question 17++++++++++++++[/!]

[q]If a cell were an office, the molecule that would act like a boss who always stays in the office would be

[c]protein

[c*]DNA

[c]RNA

[f]No. Protein is the worker molecule in the cell. Who’s the boss?

[f]Yes. DNA, in eukaryotic cells, always stays in the nucleus. That makes it somewhat like a boss who always stays in the office.

[f]No. RNA is always moving from the nucleus to the cytoplasm. If the nucleus were the office, then this analogy doesn’t fit.

[!] Question 18++++++++++++++[/!]

[q]In the diagram below, transcription is represented by which number?


[c]1   [c]2   [c]3  [c*]4     [c]5     [c]6     [c]7     [c]8

[f]No. 1 represents the cell membrane. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]No. 2 represents the nuclear membrane. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]No. 3 represents DNA. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]Yes. 4 represents transcription. During transcription, DNA information is transferred to RNA.

[f]No (but you’re close). 5 represents RNA. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]No. 6 represents the cytoplasm. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]No. 7 represents translation, or protein synthesis. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

[f]No. 8 represents a protein, which is the product of translation. During transcription, DNA information is transferred to RNA. Which number could represent this transfer?

 

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5. Next Steps