Unit 12 Study Guide

Unit 11 Study Guide(for Aosen)

Does anyone have a notes document for this unit?

Central Dogma

• Genetic information transferred from DNA → RNA → Proteins

• A gene dispatches instructions in the form of RNA, which in turn programs protein synthesis

• Coined by Francis Crick

7 Different functions of proteins

1. Structural Proteins - Provide shape and structure. Ex: Collagen

2. Contractile Proteins (Motor Proteins)  - Make your muscles and make them move. Ex: Actin and myosin.

3. Defensive Proteins - Protect the body. Ex: Antibodies.

4. Signal Proteins - Signal or regulate cellular processes. Ex: Hormones.

5. Receptor Proteins - May be built into cell membranes and Initiate cellular responses. Ex: B Cell Receptor Protein.

6. Transport Proteins - Transport resources to different parts of the cell. Ex Hemoglobin.

7. Storage Proteins - Store resources. Ex: Ovalbumin 

8. Enzymes - facilitate chemical reactions. Ex: ligase

DNA Vs. RNA

Similarities 

• Both are nucleic acids with nucleotides 

• Both contain adenine(A), cytosine(C), and guanine(G) bases

• Both have a phosphate backbone

Differences

• DNA is double-stranded, and RNA is usually single-stranded. 

• DNA contains thymine (T) as a base, while RNA uses uracil(U)

• DNA is primarily located in the nucleus, and RNA is found in the nucleus and the cytoplasm.

• DNA has deoxyribose, and RNA has Ribose 

Types of RNA and Their Functions

• Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes for protein synthesis.

• Ribosomal RNA (rRNA): Is the main component of ribosomes and helps create proteins, holds mRNA in place

• Transfer RNA (tRNA): Transfers amino acids to the ribosome during protein synthesis/translation. 

FUN FACT: tRNA folds back over itself to form a T

Location and Function of Ribosomes

Bound Ribosomes 

• Attached to endoplasmic reticulum (ER)

• They synthesize proteins for external functions

Free Ribosomes 

• Floating in the cytoplasm

• They synthesize proteins for internal functions 

mRNA Codons:

• Sequences of three nucleotides.

• Carries genetic information from DNA to ribosomes to make specific proteins.

Using the Genetic Code:

• Determines translation of mRNA codons into amino acids.

• Each codon corresponds to a specific amino acid or signal.

• Multiple codons can code for a single amino acid. (AKA redundancy).

Transcription

• Is the process of making RNA from DNA 

• Occurs in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells

RNA Polymerase 

• RNA polymerase is the enzyme that builds RNA molecules by copying a DNA template 

• RNA polymerase adds RNA nucleotides one by one to build the RNA molecule.

Where Transcription Takes Place, and Why?

• Transcription occurs where DNA is located because RNA polymerase needs access to the DNA template.

• In eukaryotic cells, transcription occurs in the nucleus because DNA is housed there.

• In prokaryotic cells, transcription occurs in the cytoplasm since they lack a nucleus.

What Is Made:

• Transcription produces messenger RNA (mRNA) molecules.

• mRNA carries the genetic instructions from DNA to the ribosome for protein synthesis.

• mRNA contains codons, which specify a protein's sequence of amino acids.

Translation

• Translation is the process of synthesizing proteins from mRNA.

• The DNA itself cannot be used since it is too large and important to leave the nucleus.

• It occurs in the cytoplasm at the ribosome.

• During translation, amino acids are brought to the ribosome by transferring RNA (tRNA) molecules and linked (with peptide bonds) to form a polypeptide chain according to the mRNA sequence.

Where Translation Takes Place and Why:

• Translation occurs in the cytoplasm because ribosomes, where translation occurs, are located in the cytoplasm.

• This location allows newly synthesized proteins to be immediately available for cell use.

mRNA Role with Codons:

• mRNA carries the genetic information from DNA to the ribosome as codons.

• Codons are sequences of three nucleotides on mRNA that specify particular amino acids.

• Each codon codes for a specific amino acid or serves as a start or stop signal for protein synthesis.

tRNA Role:

• tRNA molecules bring amino acids to the ribosome during translation.

• Each tRNA molecule carries a specific amino acid at one end and has an anticodon at the other, which base pairs with the mRNA codon.

• According to the mRNA sequence, tRNA ensures that the correct amino acid is added to the growing polypeptide chain.

rRNA Role:

• Ribosomal RNA (rRNA) is a structural component of ribosomes.

• It provides the catalytic and structural framework for protein synthesis.

• rRNA interacts with mRNA and tRNA to facilitate the correct positioning of the mRNA codon and the corresponding tRNA anticodon during translation.

Start Codon and Stop Codons - Their Importance:

• The start codon, AUG, signals the beginning of protein synthesis.

• Stop codons (UAA, UAG, UGA) signal the termination of protein synthesis.

• Start and stop codons are crucial for determining the correct reading frame and length of the protein during translation.

• Stop codons do not code for an amino acid.

Redundancy of the Genetic Code - Its Importance:

• The genetic code is redundant, meaning that most amino acids are encoded by multiple codons.

• Gene redundancy is the existence of multiple genes in an organism's genome that perform the same function.

• This redundancy provides a degree of error tolerance, as mutations in the DNA sequence may not always result in changes to the protein's amino acid sequence.

•  it minimizes the harmful effects of incorrectly placed nucleotides on protein synthesis.

• It also allows for organisms' evolutionary flexibility and adaptation to environmental changes.

Mutations

• Point Mutation/Substitution - Possibly less impact on the organism, one nucleotide is swapped out for another (one single base pair is changed, and the amino acid it codes for may not change)

• Frameshift Mutation - Adding/deleting nucleotides changed the reading from the point onward. 

• Silent Mutation - No change 

• Missense point mutation - Changes AA coding 

• Nonsense point mutation - Mutation changes codon into a stop codon ( UAG, UAA, and UGA), shortening the length of the protein.

• Missense and nonsense mutations change protein structure and function.

Causes of Mutations

Hereditary 

•  inherited from parent (must occur in gamete)

Acquired 

• It occurs in somatic cells, accumulates over time, and causes errors in DNA replication. Unless it occurs in a gamete, it affects only that organism. 

Causes 

•  Environment (Pollution, Radiation), Lifestyle (Diet, Smoking) 

•  Anything that causes mutation is called a mutagen 

Evolution 

• Silent - No evolution

• Negative mutation - hurts the survival of the organism

• Positive mutation - may help survival (special adaptation)

• No mutation -> no evolution