Protein Synthesis, Cell Division & Embryonic Development

Gene

A specific set of instructions to produce a specific protein; tells what protein to make, how to make it, when to make it, and how much to produce.

Gene expression

The process of using information in a gene to produce a functional product, such as a protein.

Transcription

The synthesis of RNA using information in DNA; produces mRNA.

Translation

The synthesis of a polypeptide using information from mRNA; occurs at ribosomes.

What is the overall flow of genetic information?

DNA → RNA → Protein.

Why does transcription occur instead of DNA being directly used to make protein?

mRNA can leave the nucleus, keeping DNA safe, and mRNA has a shorter lifespan, allowing protein production to be controlled more quickly.

What sugar does RNA contain?

Ribose.

What sugar does DNA contain?

Deoxyribose.

What base does RNA use instead of thymine?

Uracil (U).

What base does DNA use instead of uracil?

Thymine (T).

Is RNA single- or double-stranded?

Single-stranded.

Is DNA single- or double-stranded?

Double-stranded.

RNA polymerase

The enzyme that produces an RNA strand using DNA as a template.

Promoter

A sequence of DNA that signals RNA polymerase, essentially saying "start transcribing here."

Template strand

The DNA strand used by RNA polymerase to produce a complementary RNA strand.

Terminator

A DNA sequence that signals RNA polymerase to stop transcription.

What happens during transcription?

RNA polymerase binds to the promoter, uses the template DNA strand, and produces a complementary RNA strand until it reaches the terminator.

RNA processing

The process that modifies the initial RNA transcript before it becomes mature mRNA.

Introns

Intervening regions of RNA that are removed during RNA processing.

Exons

Expressed regions that remain in the RNA and are joined together.

Mature RNA

Processed RNA containing the joined exons; becomes messenger RNA (mRNA).

What happens to introns?

They are removed.

What happens to exons?

They are joined together.

Codon

A sequence of 3 mRNA bases that specifies a particular amino acid or an action by the ribosome.

How many bases are read at a time during translation?

Three bases at a time.

In what direction is mRNA read?

5′ → 3′.

Start codon

AUG; signals "start here" for translation.

What does a stop codon do?

Signals the ribosome to stop translation.

tRNA

RNA that reads the mRNA code and carries the appropriate amino acid.

Ribosome

The structure that moves along mRNA and connects amino acids together to form a growing polypeptide.

What are the three major components needed for translation?

mRNA, tRNA, and ribosome.

What does tRNA do?

Reads the codon and brings the appropriate amino acid.

What does the ribosome do?

Moves along mRNA and connects amino acids into a growing polypeptide.

What direction does the ribosome move along mRNA?

5′ → 3′.

How many nucleotides does the ribosome move at a time?

3 nucleotides, or one codon.

What is a polypeptide?

A chain of amino acids.

What are proteins made of?

Chains of amino acids.

Enzyme

A chemical catalyst that speeds up and regulates chemical reactions.

Defensive protein

A protein involved in protection against disease; antibodies are an example.

Storage protein

A protein involved in storing amino acids.

Transport protein

A protein involved in transporting substances.

Hormonal protein

A protein involved in coordinating an organism's activities; insulin is an example.

Receptor protein

A protein that allows a cell to respond to chemical stimuli.

Contractile/motor protein

A protein involved in movement.

Structural protein

A protein that provides support.

Example of an enzyme

Digestive enzymes.

Example of a defensive protein

Antibodies.

Example of a storage protein

Casein or ovalbumin.

Example of a transport protein

Hemoglobin.

Example of a hormonal protein

Insulin.

Examples of contractile proteins

Actin and myosin.

Example of a structural protein

Collagen or keratin.

Primary protein structure

The chain/sequence of amino acids produced during translation.

Secondary protein structure

A level of protein structure involving the folding of the amino acid chain.

Tertiary protein structure

The overall three-dimensional shape of a protein.

Quaternary protein structure

A protein structure formed when multiple polypeptide chains come together.

What determines a protein's 3D shape?

Its primary amino acid sequence.

Why is protein shape important?

The correct shape is required for the protein to function correctly.

Denaturation

Loss or alteration of a protein's normal shape, causing it to lose proper function.

What can cause a protein to denature?

Incorrect pH or temperature.

Reading frame

The way nucleotides are grouped into sets of three during translation.

Why is the reading frame important?

Codons must be read in the correct order and starting at the correct base.

What direction can codons be read?

5′ → 3′ only.

Mutation

A change in the DNA nucleotide sequence.

What is the most common type of mutation?

A very small change involving a single nucleotide.

What can a very large mutation involve?

An entire chromosome.

Nucleotide substitution

When one nucleotide is replaced by another.

Missense mutation

A nucleotide substitution that changes the amino acid coded for.

What can happen as a result of a missense mutation?

The resulting protein may still function correctly or may not function at all.

Nonsense mutation

A mutation in which an amino acid codon is changed into a stop codon.

What is the result of a nonsense mutation?

A truncated protein that is almost always non-functional.

Silent mutation

A mutation that causes no change to the amino acid sequence.

Why can a silent mutation occur?

Because of redundancy in the genetic code.

Frameshift mutation

A mutation that shifts the reading frame, disrupting the codons that follow.

Insertion

A mutation in which a nucleotide/base is added.

Deletion

A mutation in which a nucleotide/base is removed.

Why are frameshift mutations usually disastrous?

The shift disrupts all the codons following the mutation.

Spontaneous mutation

A mutation caused by an error during DNA replication, such as DNA polymerase failing to proofread properly.

Environmental mutagen

An environmental factor that can cause mutations.

Three types of environmental mutagens mentioned in the slides

Biological/viral, chemical, and physical.

What determines the effect of a mutation?

Where the mutation occurs.

What happens if a mutation occurs in a coding region?

It can alter protein function.

What happens if a mutation occurs in a promoter region?

The gene may be overexpressed or underexpressed.

Why are promoter mutations common in cancer?

They can cause abnormal levels of gene expression.

What usually happens if a mutation occurs in a non-coding region?

It has very little effect.

Germline cells

Cells that become gametes.

Can germline mutations be passed to the next generation?

Yes.

Somatic cells

All other cells in the body besides germline cells.

Can somatic mutations be passed to the next generation?

No.

What are characteristics of normal cells?

Distinct size and shape, distinct function, tight adherence to neighboring cells through CAMs, and 46 chromosomes.

CAMs

Cell adhesion molecules that help cells tightly adhere to neighboring cells.

What signals influence the life choices of a normal cell?

Growth factors, growth inhibitors, steroid hormones, and cell-cell interactions.

What are the possible life choices of a normal cell capable of mitosis?

Differentiation, growth/cell division, or cell death through apoptosis.

Mitosis

Cell division in which daughter cells are identical to each other and to the parental cell.

When does mitosis occur?

When cells are needed for normal growth/development, to replace dead or damaged cells, when cell surfaces aren't contacted on all sides, and when sufficient nutrients are available.

Hyperplasia

Growth caused by an increase in cell number.

Hypoplasia

Reduced development/growth due to insufficient cell growth or number.

What are the two ways tissue can grow?

Increase in cell number or increase in cell size.

What process increases cell number?

Mitosis.

Examples of mitotic tissues

Skin, intestinal lining, liver, bone marrow, and blood vessels.