Protein Synthesis & Mutations

RNA

1. Contains the sugar ribose instead of deoxyribose.

2. Single-strandedinstead of double stranded.

3. Contains uracil in place of thymine.

RNA Contains:1. Adenine2. Cytosine3. Guanine4. Uracil (not

Thymine)

Three Main Types of RNA1. Messenger RNA (mRNA) - Carries copies of

instructions, for the assembly of amino acids into proteins, from DNA to the ribosome (serve as “messenger”)

* Made in the nucleus

Three Main Types of RNA

2.Ribosomal RNA (rRNA) – Makes up the major part of ribosomes, which is where proteins are made.• Made in the nucleolus

Ribosomal RNA

Three Main Types of RNA3. Transfer RNA (tRNA) – Transfers (carries)

amino acids to ribosomes as specified by codons in the mRNA

Proteins• Proteins are made up of a chain of amino

acids.• Proteins are enzymes, which catalyze and

regulate chemical reactions.

2 Steps to Make a Protein1. Transcription

• DNA → RNA2. Translation

• RNA → Protein (Chain of amino acids)

Step 1: Transcription• Transcription - Process in

which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA.• RNA polymerase separates

the DNA strands. • One strand of DNA is used as

a template from which nucleotides are assembled into a strand of RNA.

• Occurs in the nucleus.

Transcription: DNA → RNA

After Transcription

• The mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm.

Codons• Codon - Three-nucleotide sequence on

messenger RNA that codes for a single amino acid.

The Genetic Code• The “language” of mRNA instructions is

called the genetic code. • The genetic code is read three letters at a

time, so that each “word” of the coded message is three bases long.

1.How the code is read:a. Every 3 bases on mRNA is

called a codon.b. Every codon codes for an amino

acid (building block of protein)c. Amino acids are abbreviated

most times by using the first 3 letters of the amino acid’s name.• Met = methonine• Leu = leucine

mRNA, Codons

Start and Stop Codons• Start Codons: Found at the beginning of a protein;

Only one - AUG (methionine)• Stop Codons: Found at the end of a protein; three

exist, which make the production of the protein stop: UAA, UAG,UGA

Reading the Codon Chart

Third Position

First Position

Examples:

AUG = Methionine

CAU = Histidine

UAG = Stop

Try these:

GCU:

UAC:

CUG:

UUA:

Answers:

Alanine

Tyrosine

Leucine

LeucineThis chart only works for mRNA codons!

Step 2: Translation• Translation - Decoding of a mRNA message into a

protein (amino acid chain)• Takes place on the ribosomes• Each tRNA contains:

1. An amino acid2. Three unpaired bases.

Anticodon• Each tRNA molecule has three unpaired

bases called the anticodon, which are complementary to one mRNA codon.

Steps of Translation1. Begins when an mRNA molecule in the cytoplasm

attaches to a ribosome.2. As each codon of the mRNA molecule moves

through the ribosome, the proper amino acid is brought into the ribosome by tRNA.

3. The ribosome forms a peptide bond between the first and second amino acids.

4. The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mRNA molecule and a protein has been made.

mRNA↓

t RNA

mRNA →

Start codon

Ribosome

Methionine

PhenylalanineLysine

Nucleus

Translation

Go to Section:

← Anticodon

Jan

2006

The Polypeptide “Assembly Line”

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the Polypeptide

Translation

Go to Section:

Jan

2006

Mutations• Mutation - Change in a DNA sequence that

affects genetic information; error or mistake in copying DNA.

Types of Mutations• Chromosomal Mutations

- Involve changes in the number or structure of chromosomes.Ex. Downs Syndrome

• Gene Mutations -Mutations that produce changes in a single gene.

Types of Gene Mutations1. Point Mutations - affect a single nucleotide,

or point in the DNA sequence, usually by substituting one nucleotide for another.

Original: AUGUAC → Met – TyrMutated: AUGUAG → Met – Stop(causes the amino acid chain to stop protein production early)

Types of Gene Mutations• Frameshift Mutations - Mutation that shifts the

“reading” frame of the genetic message by inserting or deleting a nucleotide.

– Insertions – A base is inserted into the DNA sequence.

– Deletions - A base is removed from the DNA sequence.

Original: The fat cat ate the wee rat.Frame Shift: The fat caa tet hew eer at.

(Frame shift mutations affect all subsequent amino acids!)

Meiosis & Genetics (Chromosomes & Punnett Squares)

Chromosomes & Genes

• Chromosome - Very long, continuous single piece of DNA, contains many genes

• Gene - Sequence of DNA that codes for a protein and thus determines a trait

• Homologous Chromosomes - Term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent.• Both chromosomes have all the same

genes in the same location, but different ‘versions’ of those genes.

Homologous Chromosomes

Haploid vs. Diploid• Haploid - Term used to refer

to a cell that contains only a single set of chromosomes and therefore only a single set of genes; “one set”; represented by N.

• Diploid - Term used to refer to a cell that contains both sets of homologous chromosomes; “two sets”; represented by 2N.

Gamete vs. Zygote• Gamete - A mature sexual reproductive cell

that has a haploid numbers that unites with another cell to form a new organism. • Example: Sperm or egg cell

• Zygote - The cell formed by the union of two gametes.

Sexual Reproduction - Process by which two cells from different parents unite to produce the first cell of a new organism.

Diploid zygote

2n+ =1n

Haploid sperm

(gamete)

Haploid egg

(gamete)

1n

Meiosis• Meiosis - Process by which the number of

chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell; Haploid (N) gamete cells are produced from diploid (2N) cells.

Produce Haploid (N) Cells

Begin with Diploid (2N) Cells

Four gametes are made during cell division by meiosis. The gamete cells have half the number of chromosomes as the original cell.

Meiosis• Meiosis usually involves two distinct

divisions:1. Meiosis 12. Meiosis 2

Meiosis 1• Prior to meiosis I, each

chromosome is replicated.• The cells then begin to divide

in a way that looks similar to mitosis.

• One big difference:• Each chromosome pairs with its

corresponding homologous chromosome to form a structure called a tetrad and exchange portions of their chromatids in a process called crossing-over.

Crossing Over• Produces new combinations

of alleles.• Meiosis 1 is similar to mitosis

except:• The two cells produced by meiosis I have sets

of chromosomes and alleles that are differentfrom each other and from the diploid cell that entered meiosis I.

Meiosis 2• Two cells produced by meiosis I now enter

a second meiotic division. • Unlike the first division, neither cell goes

through a round of chromosome replication before entering meiosis II.

• Those four daughter cells now contain the haploid number (N)—just 2 chromosomes each.

Nondisjunction• The most common error

in meiosis occurs when homologous chromosomes fail to separate.• This is known as nondisjunction.• Results in abnormal numbers of chromosomes in

gametes.• Example - Down syndrome,

which results when an individual has three copies of chromosome 21.

Mitosis vs. Meiosis• Mitosis

• Allows an organism's body to grow and replace cells. • Used in asexual reproduction to produce a new

organism. • New (daughter) cell is identical to the parent cell and

to each other.• Produces two diploid (2N) daughter cells.

• Meiosis• Used in sexual reproduction to produce gametes.• New (daughter) cells are genetically different from the

parent cells and from one another. • Produces four haploid (N) cells.• Is responsible for the genetic variation among species.

Inheritance & Cell Type• You can only inherit a trait from

gametes, not other somatic (body) cells!

• Mutations within somatic (body) cells do not affect future offspring genes. Whereas, mutations within gametes do alter offspring genes.• For example, if your mother has skin cancer, you will

not inherit this mutation because the mutation is on her somatic (body) cells and these are not inherited.

Dominant vs. Recessive

• Dominant - Masks the other trait; the trait that shows if present• Represented by a capital letter

• Recessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are present• Represented by a lower case letter

R

r

Dominant & Recessive Practice

TT - Represent offspring with straight hairTt - Represent offspring with straight hairtt - Represents offspring with curly hair

T – straight hairt - curly hair

Homozygous vs. Heterozygous

• Homozygous – Term used to refer to an organism that has two identical alleles for a particular trait (TT or tt)• Sometimes called purebred

• Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt)• Sometimes called hybrid

RR

Rr

rr

Genotype vs. Phenotype• Genotype – The genetic makeup of an organism;

The gene (or allele) combination an organism has. • Example: Tt, ss, GG, Ww

• Phenotype – The physical characteristics of an organism; The way an organism looks• Example: Curly hair,

straight hair, blue eyes, tall, green

Punnett Squares• Punnett Square – Diagram showing the gene

combinations that might result from a genetic cross

• Used to calculate the probability of inheriting a particular trait• Probability – The chance

that a given event will occur

Punnett Square

Parent

Parent Offspring

How to Complete a Punnett Square

Y-Yellowy-white

Genotype:1:2:1

(YY:Yy:yy)25%, 50%, 25%

Phenotype:3 Yellow, 75%1 White, 25%

You Try It Now!

• Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short)

TT x ttStep One: Set Up Punnett Square (put one parent on the top

and the other along the side)

T Tt

t

TT x ttStep Two: Complete the Punnett Square

T Tt

t

Tt Tt

Tt Tt

TT x tt

Step Three: Write the genotype and phenotype

T Tt

t

Tt Tt

Tt Tt

Genotype: 4 – Tt or 100%

Phenotype:100% Tall

Remember: Each box is 25%

You Try It Now!• Give the genotype and phenotype for the

following cross: Tt x tt

Tt x ttStep One: Set Up Punnett Square (put one

parent on the top and the other along the side)

T tt

t

Tt x ttStep Two: Complete the Punnett Square

T tt

t

Tt tt

Tt tt

Tt x ttStep Three: Write the genotype and phenotype

T tt

t

Tt tt

Tt tt

Genotype:Tt - 2 (50%)tt - 2 (50%)

Phenotype:50% Tall50% Short

Remember: Each box is 25%

Four Types of Chromosomal Mutations

1. Deletion – A chromosome segment is deleted or removed.

2. Duplication – A chromosome segment is duplicated or repeated

Four Types of Chromosomal Mutations

3. Inversion – A segment of a chromosome breaks off, turns around, and reattaches in the reverse order; reverses a segment within a chromosome

4. Translocation – A segment of a chromosome is moved to another chromosome.