Biology Semester 2 Freshman Year - Unit 9: Protein Synthesis

this is for the protein synthesis unit

True or False: The instructions in DNA are used to build proteins

True

What is the organelle in a cell that builds proteins?

Ribosomes

Can ribosomes “read” DNA?

No. That is why, using the Central Dogma, DNA is transcribed into RNA, which enables the ribosomes to actually “read” the RNA and use it to make proteins.

What is the monomer of a protein?

amino acid

True or False: Amino acids have unique properties that affects how the protein folds.

True

What does the amino acid sequence determine?

protein shape

What does protein shape determine?

protein function

What is the difference between DNA & RNA?

DNA:

• Double strand

• sugar = deoxyribose (DNA)

• Nitrogenous Bases: A, T, C, G

• Base Pairing Rules: A = T, C = G

RNA:

• Single strand

• sugar = ribose (RNA)

• Nitrogenous Bases - A, C, G, U (Uracil) - There is no Thymine

• Base Pairing rules: A = U, C = G

What is the Sugar Difference between DNA and RNA?

• Deoxyribose: lacks an oxygen atom on the 2’ carbon hence the “deoxy”

• Ribose: Has a hydroxyl group (-OH) on the 2’ carbon

What are the three main types of RNA?

• mRNA (messenger RNA) - carries instructions from the nucleus to the ribosomes to make proteins

• rRNA (ribosomal RNA) - makes up the ribosomes

• tRNA (transfer RNA) - brings amino acids to the ribosomes to help make proteins

What is mRNA?

Its full form is messenger RNA and it carries instructions from the nucleus to the ribosomes in order to make proteins.

What is rRNA?

Its full form is ribosomal RNA and it makes up the ribosomes.

What is tRNA?

Its full form is transfer RNA and it brings amino acids to the ribosomes to help make proteins.

What is step 1 of the Central Dogma?

Transcription (DNA to RNA)

What is the purpose of the first step in the Central Dogma (transcription)?

Segments of DNA (genes) are used as a template to create a complementary single stranded RNA molecule. This allows the instructions to build proteins to leave the nucleus.

Where does transcription occur in prokaryotes and eukaryotes?

• Eukaryotes: happens in the nucleus

• Prokaryotes: happens in the cytoplasm

What is step one of transcription?

RNA polymerase binds to a promoter

• promoter = region of DNA that represents the start of a gene

• this causes the DNA to unwind and expose a template

What happens in step two of transcription?

RNA nucleotides pair with one strand of DNA and RNA polymerase bonds the nucleotides together

• the DNA helix winds again as the gene is transcribed

What happens in step three of transcription?

The RNA strand detaches from the DNA once the gene is transcribed

• RNA then needs to be processed before it can leave the nucleus

If the DNA template strand is CGTA, then what would be the complementary RNA strand?

GCAU

• Remember: There is no Thymine in RNA, instead there is Uracil

What happens in the step four of transcription?

• Pre-mRNA molecules require editing before they are ready to be read by ribosomes

• Introns - portions that are cut out and discarded (noncoding portions)

• Exons - remaining pieces that are sliced together to form spliced together to form final mRNA

What happens in transcription?

1) RNA polymerase binds to DNA at the start of a gene (promoter)

2) Complementary mRNA strand is made from DNA template strand

3) mRNA detaches from DNA and is processed to remove introns and splice (join) exons together

What is the second step of the Central Dogma?

Translation (RNA to Protein)

What is the purpose of translation (RNA to Protein)?

It converts mRNA messages into polypeptides (proteins)

Where does translation occur?

cytoplasm / ribosomes

Amino acids are coded by what?

mRNA base sequences through codons that specify each amino acid

What is a codon?

It is a sequence of three nucleotides that codes for an amino acid.

 

If the DNA template strand showed “CGTA”, what would be the complementary RNA strand

GCAU

What is the universal code for all organisms?

the genetic code

• it matches each codon to its amino acid or function

• And since it is the universal code for all organisms

  • There are three stop codons

  • one start codon (AUG) codes for methionine

Translate this DNA strand “TAC CGT ACT” into its complementary RNA strand

AUG GCA UGA

Translate this RNA strand “AUG GCA UGA” into an amino acid sequence

Met-Ala-Stop

What are the major players of translation?

mRNA: carries the instructions of the protein to be built

Ribosome: pulls the mRNA one codon at a time

tRNA: brings amino acid to the ribosome

What happens in step one of translation?

Initiation: the ribosome comes together at the start codon of the mRNA and tRNA brings over a methionine

What happens in step two of translation?

Elongation: Ribosome “reads’’ the mRNA messages one codon at a time to help form a growing chain of amino acids

What happens in step 3 of translation?

Termination: Ribosome disassembles when it reaches a stop codon and polypeptide chain is released

• then, the polypeptide chain is folded into its functional shape

  • REMEMBER: Protein shape/fold determines protein function

• and sent to the Golgi to be modified and packaged

• Then transported to its final destination.

What organelle in the cell makes ribosomes?

nucleolus

Where are ribosomes found?

cytoplasm and rough endoplasmic reticulum

What does the Golgi do?

it modifies and packages proteins

What are the four types of protein folding?

What are examples of proteins carrying out cellular functions?

• Enzymes: Speed up reactions

• Antibodies: Fight disease

• Form structures such as hair and muscle

What happens in translation?

1) mRNA takes information from DNA to the ribosome

2) Ribosome attaches and pulls the mRNA through one codon at a time

3) tRNA brings corresponding amino acid over to the ribosome to form growing polypeptide chain’

4) Process continues until a stop codon is reached and the polypeptide is released to be modified and packaged by the Golgi

What happens in the Central Dogma (including all steps)?

Transcription: Takes a DNA message and turns it into an RNA (mRNA) message in the nucleus

mRNA modification: introns are removed and mature mRNA enters the cytoplasm

Translation: RNA (mRNA) message get read by a ribosome to build a protein

• Key players:

  • mRNA

  • rRNA

  • ribosomes

  • tRNA

What are mutations?

• Involve changes to DNA or a chromosome

• Changes to the instructions of DN can cause a protein to be made incorrectly

  • Can be beneficial and Can be harmful

But… Why do most mutations have no effect on an organism?

It is because many amino acids are coded by more than one codon in the DNA, which means that even a change in one codon still ensures that the amino acid is still being produced

True or False: Mutations can only be passed on to offspring if they occur in gametes (sex cells)

True

What are some factors that cause mutations?

• Replication errors

  • DNA polymerase has built-in proofreading function but this is not perfect

• Mutagens: environmental or chemical agent that can changes DNA

  • UV rays

  • Chemicals

  • Tobacco

  • Pesticides

What are Mutagens?

• environmental or chemical agents that can cause Mutations/change DNA

  • UV rays

  • Chemicals

  • Tobacco

  • Pesticides

What are the two types of mutations?

• Just a refresher, Mutations are changes in the DNA that may or may not affect the phenotype

• Gene Mutations: Changes to the bases in the DNA of one gene

• Chromosomal mutations: Affecting whole or part of a chromosome

What is a Gene Mutation?

Changes to the bases in the DNA of one gene

What is a Chromosomal mutation?

Affecting whole or part of a chromosome

What are the two types of gene Mutations?

• Point mutation/ substitution

• Frameshift mutation

What is point mutation/substitution?

one nucleotide is substituted for another

What is frameshift mutation?

involves insertion or deletion of a nucleotide in the DNA sequence

What affects a polypeptide more: a point mutation or a frameshift mutation?

frameshift mutation

If the original mRNA is “THE CAT ATE THE RAT”, what would the mutated RNA be regarding point mutation, if we changed the E in the first “THE” to S?

THS CAT ATE THE RAT

If the original mRNA is “THE CAT ATE THE RAT”, what would the mutated RNA be regarding frameshift mutation if we deleted the E in the first “THE”?

THC ATA TET HER AT

Do chromosomal mutations affect many genes?

Yes

What are the 4 types of chromosomal mutation?

Deletion, duplication, translocation, and inversion

What is deletion (chromosomal mutations)?

part of chromosome is deleted

What is duplication (chromosomal mutations)?

duplicates (copies) part of a chromosome

What is translocation (chromosomal mutations)?

results from the exchange of DNA segments between non-homologous chromosomes

What is inversion (chromosomal mutations)?

portion of chromosome is inverted

What are more examples of chromosomal mutations?

aneuploidy and polyploidy

What is aneuploidy?

It is a chromosomal mutation where an organism has extra or missing chromosomes

What is polyploidy?

Its is a chromosomal mutation where an organism has an extra set of chromosomes (3n, 4n, etc.)

Why does the DNA have to convert to mRNA to leave the nucleus?

because its too big

How does information flow in the Central Dogma?

DNA to RNA to Protein

Ribosomes link amino acids by forming what bonds between them?

peptide bonds

What polymer is read to make mRNA?

DNA

What is the product of translation?

polypeptide chain (protein)

The synthesis of mRNA in the nucleus, by RNA polymerase, from DNA is called _________?

transcription

Which of the following are mutagens? 

• tobacco in any form

• UV light

• man-made chemicals added to water, air, or food

all

Where on DNA, does the RNA polymerase bind to start transcription?

promotor site

What is the output or product of transcription?

mRNA

True or False: tRNA contains a codon

False (it contains an anticodon)

What is the difference between a point mutation and a frameshift mutation?

A point mutation is a single incorrect base in the mRNA sequence.

A frameshift mutation occurs when a base is added or removed causing the remaining mRNA sequence to be shifted.

How many amino acids are coded for by the strand of mRNA below? 

AUGGUACGUGGG

4 (why? - remember the codons? each codon is 3 nucleotides and each code for a specific amino acid)

Where does mRNA go after it is created?

ribosomes

Which amino acid is specified by the mRNA code UGG?

tryptophan (TRP)

Which of the following describes the process of gene expression?

• Genes are built by the nucleolus and carried out of the cell by the Golgi body.

• DNA is read by an enzyme in the nucleus, then using those instructions, the cell makes polypeptides/proteins.

• DNA is copied and then moves to the cytoplasm to make chromatin.

DNA is read by an enzyme in the nucleus, then using those instructions, the cell makes polypeptides/proteins.

Which of the following is another name for the non-coding regions that are removed from pre-mRNA, during editing, before it gets to a ribosome?

introns

The synthesis of polypeptides based on instructions from mRNA, on a ribosome is called_____?

translation

What is the name for the groups of 3 nucleotides found on tRNA?

anticodon

This is a sequence of DNA: TCACGATAC

It is transcribed into an mRNA with this sequence: AGUAGCUAUG

What mutation occurred?

insertion

Where are ribosomes produced?

nucleolus

Where do polypeptides go after being built, to get folded and packaged into proteins?

the Golgi

DNA and RNA use the same nitrogenous (made of nitrogen) bases except for one.  Which base is found in RNA but is NOT found in DNA?

Uracil (DNA has Thymine instead of Uracil)

What does the tRNA bring over to the ribosome?

a specific amino acid based on the codon