Ribonucleic Acid

 

What organelle in the cell produces proteins?

Ribosomes

 

Where are ribosomes found?

In the cytoplasm.

 

How does information carried on DNA get to the cytoplasm?

It has a helper – RNA.

 

RNA’s function: transmit information for the manufacture of proteins.

 

DNA never leaves the nucleus, but RNA does.  RNA acts as a messenger for DNA.

 

RNA’s structure: single strand of nucleotides

 

Comparison of DNA & RNA

            DNA                                                               RNA

Double stranded                                               single stranded

Deoxyribose sugar                                            ribose sugar

Nitrogen base thymine                          nitrogen base uracil replaces thymine

 

There are 3 types of RNA, all are made in the nucleus and move to the cytoplasm where proteins are made.

1.      Messenger RNA (mRNA) – single, uncoiled strand that transmits information

from DNA, used during protein synthesis (making of proteins).  Carries copy

of DNA information to the cytoplasm.  Serves as a messenger.

2.      Transfer RNA (tRNA) – single strand of RNA.  Transfers amino acids to the

      ribosome during protein synthesis.

3.      Ribosomal RNA (rRNA) – Globular form of RNA that is part of the ribosomes.

 

Making RNA – Transcription

 

Transcription is the process of transcribing DNA to mRNA

 

1. RNA polymerase (an enzyme) attaches to the DNA molecule and cause the strands of DNA to unzip.
2. RNA polymerase gathers free RNA nucleotides and helps form a complementary strand to the DNA. 
3. When RNA polymerase reaches a stop signal (a special sequence of bases), the new RNA is released from the complimentary DNA strand. 
4. The RNA moves to the cytoplasm carrying the information of the DNA with it.

 

 

 

 

 

 

How Proteins Are Made – Translation

Translation is the process by which mRNA is translated into amino acids and then into specific proteins.

• Proteins are made up of amino acids in long chains called polypeptides.
• Specific amino acid sequences are required to make each kind of protein.
• If any of the amino acids are out of order, or missing, there will be problems making the correct protein.
• DNA contains the genetic code (sequence of nucleotides) that determine the amino acid order.
• The amino acid order determines the type of protein that is made.
• The genetic code is read 3 letters at a time.  Three nucleotides hooked together are called a codon.
• Each codon codes for a specific amino acid that will be a part of the finished protein.

 

Translation Steps:

1. mRNA in the cytoplasm, move through the ribosome, the proper amino acid is brought to the ribosome and the amino acids form a polypeptide chain.
2. tRNA has an amino acid on one end and an anticodon on the other end.  The anticodon is a set of 3 bases that are complimentary to the mRNA codon.
3. The ribosome forms a bond between the 1^st and 2^nd amino acid. 
4. The 1^st tRNA is released and the ribosomes moves on down the mRNA.
5. The polypeptide chain continues to grow until it reaches a stop codon.  Then the polypeptide chain is released, and a protein has been formed.

 

Regulation of Gene Expression

Transcription of DNA can be turned on and off, depending upon the need for the protein it codes for.  Not every protein is needed at all times.

 

A repressor is bound to the DNA, preventing transcription.

 

For replication to begin, an inducer must bind to the repressor.

 

In eukaryotes, genes contain areas called introns that do not code for anything.

 

In eukaryotes, only the exons are translated into protein. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What is transcription?

 

Which nitrogen base is different in RNA than in DNA?

 

What happens to RNA before it leaves the nucleus?

 

What do you call the 3-letter set of nucleotides?

 

What does a codon code for?