Biology Module 03 Assessment

Meiosis and Mitosis

What are the two types of cell division?

Gene

Region of DNA in a chromosome that codes for a particular protein/RNA

The number varies widely (Ex. Humans have 2n = 46 chromosomes)

How many chromosomes does each species have?

Homologous Chromosomes

Pairs of chromosomes of the same type carrying the same set of genes

Ploidy

The number of complete sets of chromosomes in a cell

Haploid

One complete set of chromosomes (n)

Diploid

two complete sets of chromosomes (2n)

M Phase/Mitosis

Phase in which cell division occurs

Interphase

Phase where chromosomes uncoil into extremely long, thin structures and are growing/preparing to divide

Cell Cycle

Describes the sequence of events that leads a eukarotic cell through the duplication of its chromosome to the time it divides

G1

In this phase, the parent cell grows and generates enough organelles that the daughter cells will function normally

G2

This phase allows the cell to build the protein machinery necessary for mitosis

Mitosis

In this phase, the nucleus divides

Cytokinesis

Division of the cytoplasm

Interphase

• The cell grows and copies its DNA (includes the G1, S, and G2 phases)

• Centrosomes replicate

Prophase

• Chromosomes condense into visible chromosomes

• Spindle apparatus begins to form as centrosome move apart

Mitotic spindle

Structure made of microtubules that controls chromosome movement during mitosis

Kinetochore

• Located on the centromere’s surface

• Made of layered proteins that connect to the centromere and microtubules

• Serves as the interface between the centromere and the spindle fibers, allowing the movement and segregation of chromosomes

Centromere

• Located near the center of the chromosome (where the two sister chromatids are closely attached)

• Made of DNA

• Serves as a binding site for proteins involved in spindle fiber attachment

Prometaphase

• Nuclear envelope breaks down

• Microtubules contact chromosomes at kinetochores

• begin movement toward the metaphase plate

Metaphase

• Chromosomes complete migration to cell middle

Anaphase

• Sister chromatids separate into daughter chromosomes—pulled to opposite poles of spindle apparatus

Telophase

• Nuclear envelope reforms

• Chromosomes de-condense

Cytokinesis in Animal Cells

Actin-myosin ring causes membrane to pinch in, forming two daughter cells

Cytokinesis in Plant Cells

Microtubules direct vesicles to the center of the spindle, where they fuse to divide the cell in two

Binary Fission

Prokaryotic reproduction not involving mitosis

Cell-Cycle Checkpoints

Control point where stop and go-ahead signals regulate the cycle (default is to stop)

S-Phase

The cell makes a complete copy of its nuclear DNA and duplicates its centrosomes

G1 Checkpoint

Ensures the cell is large enough to divide, that enough nutrients are available to support the resulting daughter cells, and that DNA is undamaged

G2 Checkpoint

Ensures that DNA replication in S phase has been completed successfully, and that the MPF is present

p53 (tumor suppressor protein)

Functions by activating genes for apoptosis if DNA is damaged

M-Phase Checkpoint

Ensures that all the chromosomes are attached to the mitotic spindle by a kinetochore and that chromosomes have properly segregated

Mitosis-Promoting Factor (MPF)

A molecular signal in the cytoplasm that initiates mitosis (a protein that contains a kinase and a cyclin)

• Activates proteins involved in chromosomal condensation

• Activates microtubule-associated proteins involved in spindle formation

• Triggers the destruction of its own cyclin

Cyclin

Bind to and activate cyclin-dependent kinases to control progression through cell

Cyclin-Dependent Kinase (CDK)

Once activated, attaches phosphate groups to specific target proteins, acting like a molecular switch to turn those proteins on or off

Cancer

Uncontrolled cell division due to mutations in genes that contain the information for proteins that promote or prevent cell division.

Proto-oncogenes

Promote cell division (gas-pedal)

Oncogenes

Mutated proto-oncogenes that drive nonstop cell growth

Tumor Supressor Genes

Contain information that halt cell division (brakes)

Avery, McCarty, and MacLeod

Found that…

• DNA is required for the transformation of harmless bacteria into pathogenic bacteria

• Neither RNA nor protein is necessary for the transformation of harmless bacteria into pathogenic bacteria

Phosphate Group, Sugar, Five-Carbon Sugar

What are the three components of a nucleotide?

Phosphodiester Bonds

Bonds between DNA/RNA nucleotides

Phosphate (5’) to Hydroxyl (3’)

In which direction are strands written/read?

Origin of Replication (ORI)

A specific sequence of DNA to which proteins required to start DNA replication attach

Eukaryotic cells have multiple ORIs; Prokaryotic cells have one ORI

What is different about the ORIs of eukaryotic vs prokaryotic cells?

Allow a chromosome to be replicated more rapidly

What is the benefit of having multiple ORIs?

Replication Fork

Where DNA opens up on one side of a replication bubble

• Starts at the ORIs

• BOTH strands are copied at the same time in BOTH directions

• Formation of new strands requires a template

• New strands are complementary to the template strand

• Formed in specific direction (P-OH)

What are the five basic mechanisms of DNA replication?

Leading Strand

Strand formed in one piece towards the replication fork (away from the ORI)

Synthesized discontinuously in short segments moving away from the replication fork

DNA Helicase

Unwinds DNA strands

Topoisomerase

Breaks and rejoins the DNA double helix to relieve twisting forces caused by the opening of the helix

DNA Polymerases

• Form new strands by adding complementary nucleotides (two at each replication fork

• Require a template DNA strand and an RNA primer to start new strands

• Able to proofread (remove and replace incorrect nucleotides added during DNA replication

RNA Primer

• Short piece of RNA

• Formed by primase-RNA-polymerase

• Removed and replaced with DNA by other enzymes after a new strand is started

5’ (P) to 3’ (OH)

In what direction does DNA polymerase form new strands?

DNA Ligase

Links pieces of a new DNA strand together by forming phosphodiester bonds (not needed for the leading strand)

Replisome

The large macromolecular machine the enzymes required for DNA synthesis are organized in

Gene Expression

The process of using the information stored in DNA to make specific products that actually do things in the cell (polypeptides or functional RNAs)

Transcription

Making an RNA copy of a gene (first step in expressing all genes)

Translation

Using an RNA message (mRNA) to direct the formation of a polypeptide (only required for the expression of genes that contain information to make proteins)

Genome

All the genetic infomration (DNA) in a cell

Chromosome

A single DNA molecule that is part of the genome (has many genes)

Gene

Sequence of DNA that contains the information to make a functional product (protein or function RNA)

DNA to RNA to Protein

What is the central dogma?

Many genes code for RNA molecules that are not translated into proteins

Modifcations to the central dogma

3

How many amino acids specify an amino acid (codon)?

1

How many amino acids does each codon correspond to?

Unambiguous

One codon corresponds to (specifies) one amino acid

Redundant

More than one codon for an amino acid (except Met and Trp)

Redundancy

What feature of genetic code reduces the chance that a change in the DNA or mRNA sequence will alter the amino acid sequence generated by translation?

AUG

What is the start codon

Met

What does AUG code for

None

What amino acids do stop codons code for?

Codons do not overlap

What feature of genetic code minimize the chaance that a change in the DNA or mRNA sequence will alter the polypeptide sequence?

5’ (P) to 3’ (OH)

What direction are mRNAs translated in?

Promoter

Specific sequence of DNA that indicates the start of a gene (start signal)

Terminator

Specific sequence of DNA that marks the end of a gene (stop signal)

Characteristics of RNA polymerase

• Synthesizes RNA from DNA

• Builds RNA in the 5’ to 3’ direction

• Does NOT require a primer

• Bacteria have one, eukaryotes have three distinct types

Initiation (DNA Replication)

• Helicase unwinds the double helix at ORIs, creating replication forks

• Topoisomerase relieves tension from unwinding

• Primase synthesizes short RNA primers to provide a free OH (3’) group, providing a necessary starting point for DNA polymerase

Prokaryotic Initiation (Transcription)

• Sigma factor binds to RNA polymerase, forming a holoenzyme

• The holoenzyme/RNA polymerase binds to a promoter (typically containing a -35 box and -10 box)

Eukaryotic Initiation (Transcription)

• A general transcription factor binds to one of three types of RNA polymerase, forming a holoenzyme

• The holoenzyme/RNA polymerase binds to a promoter (larger and more variable, often including a TATA box -30)

Elongation (Transcription)

• RNA polymerase moves in the 3’ to 5’ direction along the template DNA strand

• A complementary RNA strand is formed from 5’ to 3’

• Covalent bonds link nucleotides in the new RNA strand

Termination (Transcription)

• RNA polymerase transcribes a terminator sequence—signals RNA polymerase to stop

• RNA polymerase and the mRNA strand are released from DNA template

• Termination proteins facilitate release in some bacteria

Introns

Intervening sequences in eukaryotic genes (are not translated)

Exons

Protein-coding regions in eukaryotic cells (are expressed)

RNA Splicing

Only occurs in the nucleus of eukaryotes; the process of introns being removed by snRNPs

Helps protect mRNA from being degraded

In eukaryotes, what is the purpose of the addition of caps and poly-A tails (long chains of adenines)?

Translation

The biological process by which a cell uses the genetic code carried by a messenger RNA (mRNA) molecule to build a specific protein

Transcription

The process where a cell makes an RNA copy of a specific DNA sequence (gene)

tRNAs

• Adaptors between mRNA codons and amino acids (40 types)

• Only one type attaches to one type of amino acid

• None complementary to stop codons

Aminoacyl tRNA

When a tRNA has an aa attached

Anticodon

The three nucleotides of tRNA that interact with complementary mRNA codon

• Many amino acids are specified by more than one codon

• Codons for the same amino acid tend to differ only in the third position

Why don’t cells need 61 different tRNAs?

Aminoacyl-tRNA Synthetases

• Determine which amino acid is paired with which anticodon; Thus, what amino acid is paired with which anticodon

• “Set” the genetic code in cells

• Highly accurate

Ribosomes

• Complexes of proteins and RNAs that form polypeptides

• Help position mRNAs and tRNAs carrying amino acids

• Form covalent bonds between amino acids

Initiation (Translation)

Ribosome and first tRNA assemble at the start codon

Elongation (Translation)

Polypeptide chain formed as ribosome moves along the mRNA

Termination (Translation)

• A stop codon is reached

• Component disassembles

• Ribosome (unchanged)

• mRNA (unchanged)

Mutation

• Permanent change in the DNA sequence of an organism’s genome

• Source of genetic diversity (creates new alleles)

• Does not always change the amino acid sequence of a polypeptide

Substitution Mutations

Mutations that change one base-pair