Jonah | Biology Topic J

Protein & its Functions

in charge of the expression of our traits (hair/eye color, ability to make insulin, predisposition for cancer, etc.)

Amino Acids

• structural building blocks of proteins, linked by peptide bonds

• put together in different orders according to the groups of 3 nitrogen bases in DNA (called codons)

DNA

• holds the code (instructions for making proteins)

• found in the nucleus of cells, but proteins are made on ribosomes

RNA

• made of nucleotides

• like DNA, except

  • single stranded, not double

  • ribose sugar, not deoxyribose

  • Uracil (U), not Thymine (T)

mRNA

• messenger RNA

• carries the code from DNA out of the nucleus to the ribosomes

rRNA

• ribosomal RNA

• binds to mRNA and reads the code

tRNA

• transfer RNA

• delivers amino acids to the ribosome to assemble the protein

“Central Dogma”

DNA → RNA → Protein

• transcription = DNA code is transcribed into mRNA molecule and leaves the nucleus

• translation = mRNA code is read at the ribosome and used as instructions to make a protein

Nitrogen Bases

A(denine)

C(ytosine)

T(hymine)

G(uanine)

Transaction Steps

1. DNA double helix “unzips”

2. Free RNA nucleotides form base pairs using the original DNA strand as a template (A-U and C-G)

3. The mRNA strand breaks away and leaves the nucleus carrying the genetic code with it

Translation Steps

1. mRNA makes its way out of the nucleus into the cytoplasm

2. Protein factories in the cytoplasm (called ribosomes) bind to the mRNA

3. The ribosome reads the code on the mRNA to produce a chain made up of amino acids

4. Transfer RNA (tRNA) molecules carry the amino acids to the ribosome

5. The mRNA is read 3 bases at a time (codon)

6. As each codon/triplet is read, a tRNA delivers the corresponding amino acid, adding it to a growing chain of amino acids, which is folded into a protein

Ribosome

• protein factories in the cytoplasm

• acts as the site of protein synthesis (translation)

Nucleus

ribosomes get their orders for protein synthesis from the nucleus, where portions of DNA are transcribed to make mRNA

Codon

a sequence of 3 consecutive nucleotides in mRNA that acts as a unit of genetic information, coding for a specific amino acid or a stop signal during protein synthesis

Mutation

a change in an organism’s DNA sequence

Mutation in Sex Cells

change in an organism’s DNA sequence that can be passed to off offspring

Mutation in Body Cells

change in an organism’s DNA sequence that cannot be passed to offspring, BUT could impair the function of the cell or cause disorders

Point Mutation

substitution of one or more nitrogenous base in a gene

• changes ONE nucleotide

• MAY change one amino acid

• sickle cell disease is the result of one nucleotide substitution

Frameshift Mutation

insertion or deletion of one or more nucleotides

• changes the “reading frame” like changing a sentence

• large sections of proteins are built incorrectly

Chromosomal Mutation

involves large sections of chromosomes

• many nucleotides are deleted, copied, or relocated

• massive changes to the organism may result

Silent Mutation

does not cause change in the organism

• several codons can code for the same amino acid

• results in same protein being built

Mutagens

agents that cause genetic mutations

Mutagen Examples

• radiation (X-rays, ultraviolet (UV) light, and nuclear radiation_

• chemicals (asbestos, benzene, formaldehyde)

• high temperatures

Which of the following is NOT true of RNA?

it has thymine

A possible mutagen is

x-ray

Transcription takes place in the

nucleus

mRNA molecules are transcribed from

DNA

What does the “m” in mRNA stand for?

messenger

Mutations are important to the evolution of species because they:

cut out and replace damaged or useless genes

rRNA is found in the

ribosome

Which type of mutation would cause the most changes to an organism?

chromosomal mutation

What molecule carries protein-making instructions out of the nucleus to the ribosome?

mRNA

How many codons are there in a chain of 18 nucleotides?

6