Transcription and Translation

S. HS. 3.2.1

DNA

• DNA (DeoxyriboNucleic Acid) is the information for life; it is made of repeating nucleotides and appears as a twisted ladder shape (double helix). Watson and Crick are responsible for developing a model of this structure.– Nuleotides of DNA consist of:

1.)deoxyribose-5 carbon sugar

2.)phosphate

3.)1 nitrogen base-adenine, guanine, cytosine, or thymine

DNA

• The nitrogen bases form the steps on the ladder or rungs of the ladder; they do this by pairing with their compliment– A pairs with T– C pairs with G

●A nucleotide is named according to the base it contains

♦phosphate and sugar form the backbone(sides) of ladder

♦nitrogen bases stick out like teeth on a zipper

(picture)

DNA

• Before a cell can divide, DNA must make a copy of itself (DNA Replication)

• Without this process, new cells only have half the DNA of their parents

• With this, the genetic makeup of an organism can be passed to new cells during mitosis or to new generations through meiosis followed by sexual reproduction.

DNA to Protein

• The sequence of nucleotides in an organism is the genetic code of an organism and can be converted to a sequence of amino acids in proteins.

• RNA like DNA is a nucleic acid, like DNA. It too is made up of nucleotides►3 major differences:

1.)RNA is single stranded-DNA is double2.)RNA has ribose-DNA has deoxyribose3.)RNA has uracil-DNA has thymine

(picture)

Transcription

• DNA → mRNA(in nucleus) (leaves nucleus, goes to ribosome)

◊Transcription (rewriting the code) takes place in the cell’s nucleus where enzymes make an RNA copy of a DNA strand; mRNA is made.

◊This process is similar to DNA replication except that the result is one single stranded RNA molecule.

Transcription

◊ DNA unzips first, then free floating RNA nucleotides pair with their complimentary DNA nucleotides on one DNA strand

◊ When pairing is complete, mRNA breaks away and leaves the nucleus

Translation

• mRNA → protein(nucleotides) (amino acids)■ Translation is the process of converting the info in

mRNA into an amino acid sequence ■ Translation takes place at the ribosomes in the

cytoplasm. ■ All organisms use the same amino acids, making the

genetic code universal.

Transcription and Translation• If one DNA strand has the base sequence G C T A A T G C A, the other

strand is _ _ _ _ _ _ _ _ _ (its compliment)

• Once you have found the compliment, the mRNA strand must be completed.• After the mRNA is complete, the codons can be underlined.• The codons can then code for an amino acid.

For instance, using the above strand, the process would appear as this:

DNA G C T A A T G C ACS C G A T T A C G TmRNA C G A U U A C G U A.A. Arg Leu Arg

Mutations• Mutations are changes in DNA; these are natural processes that produce

genetic diversity in organisms

• There are different types of mutations– Point or Substitution Mutation= a single nucleotide is replaced by another of the

three nucleotidesDNA T A G G C A

(m)DNA T A C G C A *Notice two amino acids will still be coded – Frameshift Mutation= a single nucleotide is inserted or deleted into the DNA

strand; when this occurs, the reading of the amino acids will shift to the right or left respectively by one base

DNA T A G G C A - Italicized G is deleted (m)DNA T A G C A *Notice only one amino acid will be coded

DNA T A G G C A – An adenine nucleotide is added (mDNA) T A G G A C A – *Notice that still only two amino acids can be formed

because a codon must include three nucleotides in order to form an amino acid

Transcription and Translation Questions

1.) A base sequence is shown below.ACAGTGC

How would the base sequence be coded on mRNA?A TGTCACGB GUGACAUC UGUCACGD CACUGUA

Transcription and Translation Questions

2.) A scientist puts nucleotide chains of UUUUUU in a test tube under conditions allowing protein synthesis. Soon the test tube is full of polypeptide chains composed of only the amino acid phenylalanine. What does this experiment indicate?A The amino acid phenylalanine is composed of uracil.B UUU codes for the amino acid phenylalanine.C Protein synthesis malfunctions in test tubes.D Most proteins contain only one type of amino acid.

Transcription and Translation Questions

3.) 5’ ATCAGCGCTGGC 3’

The above sequence of DNA is part of a gene. How many amino acids are coded for by this segment?

A 4

B 8

C 12

D 20

Transcription and Translation Questions

4.) A strand of mRNA containing the repeating sequence AAGAAGAAGAAG could code for which of the following amino acid sequences?

A lys-arg-glu-lys

B ser-ser-glu-glu

C lys-arg-lys-arg

D lys-lys-lys-lys

Transcription and Translation Questions

5.) Although there are a limited number of amino acids, many different types of proteins exist because theA size of a given amino acid can vary.B chemical composition of a given amino acid can vary.C sequence and number of amino acids is different.D same amino acid can have many different properties.

Transcription and Translation Questions

6.) 5’ G T A _ _ _ A A 3’ 3’ C A T G C A T T 5’ This segment of DNA has undergone a mutation in which three nucleotides have been deleted. A repair enzyme would replace them with

A CGT.B GCA.C CTG.D GTA.

Mutations

7.) Which of these would most likely cause a mutation?A the replacement of ribosomes on the endoplasmic reticulumB the insertion of a nucleotide into DNAC the movement of transfer RNA out of the nucleusD the release of messenger RNA from DNA

Mutations

8.) Mutations within a DNA sequence areA unnatural processes that are harmful to genetic diversityB unnatural processes that always affect the phenotypeC natural processes that always affect the phenotypeD natural processes that produce genetic diversity

Genetic Engineering Questions

9.) The bacterium Agrobacterium tumefaciens infects plants, and a portion of its DNA is inserted into the plant’s chromosomes. This causes the plant to produce gall cells, which manufacture amino acids that the bacterium uses as food. This process is a natural example ofA hybridization.B grafting.C genetic manipulation.D polyploidy

Genetic Engineering Questions

10.) Genetic engineering has produced goats whose milk contains proteins that can be used as medicines. This effect was produced by

A injecting foreign genes into the goats; udders.

B mixing foreign genes into the milk.

C inserting foreign genes into fertilized goat eggs.

D genetically modifying the nutritional needs of the goat’s offspring.

Slide Answers

1) C 6) A

2) B 7) B

3) A 8) D

4) D 9) C

5) C 10) C