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How Does DNA Control Gene Expression?

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by

Kevin Goodenough

on 13 February 2014

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Transcript of How Does DNA Control Gene Expression?

How Does DNA Control Gene Expression?
RNA & the Basics of Gene Expression
(Remember - Chromosomes are composed of genes which are composed of specific sequences of DNA)
Transcription
- The first step of gene expression is a process called
transcription
.

- This is where RNA is made from the information in DNA.
- Think of transcription like copying (transcribing) notes from the presentation (DNA) onto this note sheet (RNA).
-
Transcription takes place in the cell nucleus.

- Information in a specific region of DNA (a particular gene) is transcribed, or re-written, into RNA in 3 steps:
CODONS
Codons are short segments of RNA that contain three nucleotides (1 nucleotide = sugar, phosphate, base).
Each codon codes for one of twenty different amino acids. The system of matching codons to amino acids is called the Genetic Code!!
The genetic code is based on codons that each represent a specific amino acid.
Strands of linked amino acids make up proteins.
- Gene expression is the most fundamental level of how the
genotype
produces the
phenotype
.
- Gene expression turns genes into specific traits. There are 2 processes needed in order for genes to produce proteins, they are called
transcription
and
translation
.
Both processes need to occur before proteins can be made.
If proteins are not made or are made incorrectly, we do not function properly.
- Both of these processes require the use of RNA. RNA stands for
ribonucleic acid
and it is present in all living cells.
- RNA does not have Thymine, it pairs
Uracil
with
Adenine

- RNA is very similar to DNA but also different in a few key ways.
Similarities
- 4 bases
- Composed of nucleotides
- Carries information

Differences in RNA
- Single stranded
- Contains Uracil, not Thymine
- Contains Ribose sugar
- Made from transcribed DNA
- Used in translation

Differences in DNA
- Double stranded
- Contains Thymine, not Uracil
- Contains Deoxyribose sugar
- Provides the template for RNA

DO NOW QUESTION
Start of Transcription
• Transcription starts when the enzyme RNA polymerase binds to the beginning of the DNA sequence on the gene called the promoter. The promoter is the only place where transcription can start.
Final Step in
Transcription
• Next RNA polymerase adds complementary bases to the separated DNA strand and starts to form a single strand of RNA.
Once the RNA polymerase reaches a “stop” sequence, the entire RNA strand releases from the DNA and the DNA closes up and re-forms the double helix.
The Second Step
of Transcription
• The RNA polymerase unwinds and separates the DNA double helix and starts the production of RNA.
Just a small section of DNA gets unwound at a time
DO NOW
Question
after
video
Think of the start codon like a capital letter at the beginning of a sentence and stop codon like the period at the end of a sentence.
Translation
The second step of gene expression is a process called
translation
.
Translation takes the information within the single strand of RNA, in the form of codons, and
translates it into a very specific protein.

Think of translation like translating a sentence from your Spanish class into English. The information is written in Spanish (RNA) and translation translates it into English (protein).
Translation occurs in the cytoplasm of the cell, outside of the nucleus.
Each codon on the
RNA translates to one amino acid
. As translation occurs, each amino acid becomes connected along a strand and, when a codon meaning “Stop” is reached, the newly formed protein is complete!
Warm Up Question:
Why would collecting DNA evidence, like this project did, help count how many different/unique grizzly bears there are in Montana?
(Think about the uniqueness and individuality of DNA.)
Exit Question: What does Mr. Goodenough mean when he says "Gene Expression?"
If errors occur during translation or transcription, incorrect codons will be produced and a deformed protein will result.
Homework: Page 136-138, Honors Page 139
RNA: Uracil = RED
Purple
Remember, RNA is SINGLE stranded, not DOUBLE standed like DNA.
This is DNA, not RNA!!
Warm Up
Work with a neighbor and quietly discuss the following practice questions.
When finished, we will regroup and go over the question before moving on.
1) A nitrogenous base, phosphate, and sugar make up a:
A) Protein
B) Nucleotide
C) Polymerase
D) Hydrogen Bond

2) This enzyme unwinds DNA and breaks apart the hydrogen bonds:
A) DNA Polymerase
B) RNA Activase
C) RNA Splitase
D) DNA Helicase
3) The process of making a copy of DNA is:
A) Write 3 incorrect responses
B) and 1 correct reponse
C)
D)


4) Write your own question with responses.
A)
B)
C)
D)



DNA Jeopardy
Teams of 4
Each team will need a white board and a DRY ERASE marker
The teacher will select the best behaved group to pick the first question
The question will be read, then teams will have 30 seconds to discuss and write their answer
AFTER the teacher says, hold up your team's answer
If correct, you get the points.
Final Question your team will get 2 minutes to respond
Teams can wager as many points as they have on the Final Question
Full transcript