8.4 Transcription TEKS 4B, 6C, 9C

The student is expected to:

4B investigate and explaincellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules; 6C explain the purpose and process of transcription and translation using models of DNA and RNA; 9C identify and investigate the role ofenzymes

What is a gene?

• A gene is a set of DNA instructions that control the synthesis of proteins within the cell.

• This process, called protein synthesis, involves 2 steps: transcription and translation.

8.4 Transcription TEKS 4B, 6C, 9C

RNA carries DNA’s instructions.

• The central dogma states that information flows in one direction from DNA to RNA to proteins.

8.4 Transcription TEKS 4B, 6C, 9C

• The central dogma includes three processes.

• RNA is a link between DNA and proteins.

replication

transcription

translation

– Replication– Transcription– Translation

Central Dogma of Molecular Biology

• DNA cannot leave the nucleus, so a copy is made in the form of a similar nucleic acid called RNA (ribonucleic acid) during transcription.

• After DNA is used to make RNA, the RNA is then used to make proteins during translation by ribosomes in the cytoplasm.

How is DNA different from RNA?

1. RNA contains the sugar ribose and DNA contains the sugar deoxyribose

2. RNA is single-stranded, DNA is double-stranded

RNA has uracil instead of thymine..

3. RNA contains uracil instead of thymine. Uracil, like thymine, is a pyrimidine (contains one ring).

RNA is similar to DNA:4. RNA and DNA are both a

nucleic acid macromolecule.

5. RNA is made of nucleotides.

3. Both DNA and RNA have adenine, cytosine, and guanine.

How is DNA different from RNA?

Three types of RNA1. messenger RNA

(mRNA): • carries a copy of

the information in DNA.

• This type of RNA acts as a “messenger” bringing the information in the DNA to the ribosome.

2. ribosomal RNA (rRNA):

• Found within ribosomes.

( Recall that ribosomes synthesize proteins.)

• Ribosomes are made of both proteins and rRNA.

2 subunits

3. transfer RNA (tRNA):

• Brings amino acids to the ribosome to be added to the polypeptide chain that is being made at the ribosome.

• There is one tRNA for each of the 20 amino acids.

Label this figure on your notes!

Transfer RNA

anticodon

tRNA

Amino acid

Transcription-

Click on the picture for video

Transcription(In the nucleus)

Transcription is the process in which the nucleotide sequence of DNA is copied, within the nucleus, into a complementary nucleotide

sequence of RNA. DNA mRNA

TranscriptionStep 1: • The enzyme RNA

polymerase binds to the DNA and separates the 2 DNA strands.

Step 2: • RNA polymerase uses only

one strand of DNA as a template to make a complementary RNA strand.

• RNA Polymerase reads 3’ 5’

• DNA is like the “master plan” and mRNA is like the “blueprint.”

• The master plan stays in the office (the nucleus) and the blueprint can be taken to the construction site (the ribosome).

Step 3

RNApolymerase

DNARNA

How does RNA look different than DNA?Do RNA and DNA leave the nucleus?

Once RNA is made, the RNA detaches from the template strand, leaves the nucleus through nuclear pores, and enters the cytoplasm of the cell and fo to a ribosome

• Cells have the ability to control what genes are expressed and how often they need to be transcribed.

• Cells will cut out pieces from the mRNA that they do not wish to use or add promoters before a particular gene so it is transcribed more often.

Practice with Transcription

• If this is the given DNA strand:

ATGCGATCGAGCGAA

Write out the complementary mRNA strand made during transcription

UACGCUAGCUCGCUU