UNIT 7DNA Structure, Replication, and

Protein Synthesis

Section 3 Objectives● Describe the difference between DNA and

RNA. ● Define transcription. ● Define translation. ● Apply to rules of base pairing to replicate,

transcribe, and translate a strand of DNA.

RNA and Protein Synthesis

● Genes are coded DNA instructions that control the production of proteins in the cell.

● In order to decode genetic messages, part of the nucleotides must be copied from DNA to RNA

● WHY??? ● RNA are molecules that carry information for making

proteins. ● Proteins help to display our genetic traits or, in other

words, our genotype affects our phenotype.

● What is RNA?

● RNA: ribonucleic acid ● Contains information for making proteins.

● A “disposable copy” of a segment of DNA

● In RNA, Uracil (U) replaces Thymine (T).

How are DNA and RNA Different?

DNA RNA

Sugar is deoxyribose Sugar is ribose

double stranded single stranded

A,C,G,T A,C,G,U

● 3 types of RNA:

1. Messenger RNA (mRNA) -carries the instructions or “message” for making

amino acids which will then become proteins.

2. Ribosomal RNA (rRNA) -makes up ribosomes -remember that ribosomes make proteins!

3. Transfer RNA (tRNA) -RNA transfers each amino acid to the ribosome -these amino acids make up our proteins in the cell

● Each type of RNA has a specific job in making proteins.

● Steps to making proteins:

DNA RNA proteins

● Transcription: DNA to mRNA ● process in which a portion of the DNA strand is

written (script means to write!) into a complementary strand of RNA (mRNA)

● This occurs in the NUCLEUS!! ● remember… U replaces T

EXAMPLE:

DNA says=A T T G C T A C G G TRANSCRIBES INTO… mRNA writes=U A A C G A U G C C

RNA polymerase is the enzyme that “unzips” the DNA during transcription so it can be read and allow a complementary mRNA strand to be created. Transcription occurs from the 5’ (said “five prime”) to 3’ direction.

● Once the mRNA has the information, it leaves the nucleus (because the DNA cannot) and enters the cytoplasm.

● Let's watch it in action! (video is 1:52)

● The original DNA strand is transcribed into mRNA.

● REVIEW: ● DNA to DNA = replication AAGCAT TTCGTA

● DNA to RNA = transcription AAGCAT UUCGUA

● Translation: RNA to protein ● This is the decoding of an mRNA message into a

protein……it is “translated”

● Occurs ON the Ribosomes which is IN the CYTOPLASM

● Ribosomes are responsible for “reading” the mRNA sequence and assembling proteins.

RNA !Proteins: Translation

● The “language” of mRNA is called the genetic code.

● How do you break the code? ● The code is read 3 letters at a time ● This is a codon: a three letter sequence of

nucleotides that codes for an amino acid. ● Amino acids make up proteins.

● Example:-the bases would be read 3 letters at a time.

UCGCACGGU This would be read as.. UCG--CAC--GGU

● Each codon represents a different amino acid

● How do you determine the amino acid?

*to read start in the middle and work outwards.

*EXAMPLE:

UCA = Serine

* notice there are stop codons

*the start codon is AUG

● Each codon of the mRNA moves through the ribosome

● The proper amino acid is then brought into the ribosome by the tRNA.

● Each tRNA carries one amino acid. ● Each tRNA has an anticodon: 3 base pairs

that are complementary to one mRNA codon.

•As the ribosome moves down the mRNA, each amino acid is attached in a chain called a polypeptide chain

•The old tRNA is released and a new tRNA is brought in.

•The amino acid chain grows until the ribosome reaches a stop codon. Let's watch! (2:04)

● How much DNA is there and what is it all for? (1:02)

• Some sections of DNA code for a protein and some sections do not.

• Exons are sections of DNA that code for proteins.

• Introns are sections of DNA that DO NOT code for proteins.

How do introns get "edited" out? (2:51)

● REVIEW: ● DNA to DNA = replication AAG-CAT TTC-GTA

● DNA to RNA = transcription AAG-CAT UUC-GUA

● mRNA to amino acids = translation mRNA Strand- UUC GUA

tRNA carrying Amino Acids-AAG (phenylalanine)-CAU (valine)

Let’s Check ● Transcribe and Translate the following DNA: TAC—CCG---TAA---GAC---AAC----GTT

mRNA: AUG—GGC---AUU---CUG---UUG---CAA Amino acid: methionine—glycine---isoleucine---leucine---leucine---glutamine

● What would be the complementary strand of tRNA?

UAC---CCG---UAA---GAC---AAC---GUU

Section 4 Objectives● Define mutation. ● Describe the different mutations that can

occur in our DNA

Mutations● Mistakes can happen in the cell ● We call these mutations: changes in the

genetic material. ● Almost all mistakes or mutations in our DNA are

neutral or have little or no effect. ● Some mistakes can be beneficial for an

organism ● Some, however, can cause serious genetic

disorders

● Types of mutations: 1. Point mutations

- Occurs in one or a few nucleotides. - One base can be added, deleted, or substituted

Examples of Point mutations: -Substitution: THE---FAT---CAT---ATE---THE---RAT THE---FAT---CAR---ATE---THE---RAT -Insertion/Addition: THE---FAT---CAT---ATE---THE---RAT THE---FAT---CAT---HAT---ETH---ERA---T -Deletion: THE –- FAT—CAT—ATE—THE –RAT TEF—ATC—ATA—TET---HER-AT

2. Frameshift mutations - When the reading frame of the sequence is

changed due to addition or deletion of a nucleotide.

Example: -Insertion/Addition: THE---FAT---CAT---ATE---THE---RAT THE---FAT---CAT---HAT---ETH---ERA---T -Deletion: THE –- FAT—CAT—ATE—THE –RAT TEF—ATC---ATA---TET---HER

3. Chromosomal mutations - Changes in the number or structure of

chromosomes

INVERSION

DELETION

ADDITION

Are you getting it? Use a separate sheet of paper and turn in!

1. The process of copying DNA is called____. 2. Where does replication take place? 3. When would replication occur?

4. The process of copying DNA into RNA is called__________. 5. The process of making proteins from RNA is called________. 6. Transcribe and translate the following DNA strand:

TAG—GGC---CAT---TAC mRNA= ______________ amino acids= ___________

BONUS: Write your name in codon form……… example: MICHAEL would be MIC---HAE---L Then rewrite it showing a point mutation.

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