Module B Review

Module B Review

Part One

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Cells divide at different rates.• The rate of cell division varies with the need for that type

of cell.

• Some cells are unlikely to divide (in Gap 0/G0 of the cell cycle)– Example: neurons

Cell size is limited.• Volume increases faster than surface area.

– Cells need to stay small to allow diffusion and osmosis to work efficiently.

Mitosis and cytokinesis produce two genetically identical daughter cells.

• Interphase prepares the cell to divide.

• During interphase, the DNA is duplicated.

Mitosis divides the cell’s nucleus in four phases.

• Prophase– Chromosomes condense, spindle fibers form, and

the nuclear membrane disappears


• Metaphase– Chromosomes line up in the middle of the cell


• Anaphase– Sister chromatids are pulled apart to opposite

sides of the cell


• Telophase– Two nuclei form at opposite ends of the cell, the

nuclear membranes reform, and the chromosomes uncoil back into chromatin

Cytokinesis differs in animal and plant cells.

• Cytoplasm separates– Animal cells: membrane pinches

the two new cells apart– Plant cells: a cell plate (new cell

wall) separates the two new cells

Cell division is uncontrolled in cancer.• Cancer cells form disorganized clumps called

tumors.– Benign tumors remain clustered and can be

removed.– Malignant tumors metastasize, or break away, and

can form more tumors.

5.4 – Asexual Reproduction

• Key Concept:– Many organisms reproduce by cell division.

Binary fission is similar to mitosis.• Asexual reproduction is the

creation of offspring from a single parent.– Binary fission produces two

daughter cells genetically identical to the parent cells.

– Binary fission occurs in prokaryotes.

Some eukaryotes reproduce by mitosis.

• Budding forms a new organism from a small projection growing on the surface of the parent.

• Fragmentation is the splitting of the parent into pieces that each grow into a new organism.

• Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

Multicellular organisms depend on interactions among different cell types.• Tissues are groups of cells that perform a similar

function.• Organs are groups of tissues that perform a specific

or related function.• Organ systems are groups of organs that carry out

similar functions.

Specialized cells perform specific functions.

• Cells develop into their mature forms through the process of cell differentiation.

• Cells differ because different combinations of genes are expressed.

• A cell’s location in an embryo helps determine how it will differentiate.

6.1 – Chromosomes & Meiosis

• Key Concept:– Gametes have half the number of chromosomes

that body cells have.

You have somatic cells and gametes.

• Somatic Cells:– Are body cells– Make up all cells in body except for

egg and sperm cells– Not passed on to children

• Gametes:– Are egg or sperm cells– Passed on to children

Your cells have autosomes and sex chromosomes.

• Somatic cells have 23 pairs of chromosomes (46 total)– (1) Autosomes: pairs 1 – 22; carry

genes not related to the sex of an organism– (2) Homologous chromosomes: pair of chromosomes; get one from each parent; carry the same genes but may have a different form of the gene (example: one gene for brown eyes and one gene for blue eyes)

– (3) Sex chromosomes: pair 23; determines the sex of an animal; control the development of sexual characteristics

Somatic cells are diploid; gametes are haploid.

• Diploid (2n)– Has two copies of each

chromosome (1 from mother & 1 from father)• 44 autosomes, 2 sex

chromosomes– Somatic cells are diploid– Produced by mitosis

• Haploid (1n)– Has one copy of each

chromosome• 22 autosomes, 1

sex chromosome– Gametes are haploid– Produced by meiosis

Meiosis I• Occurs after DNA has been replicated

(copied)• Divides homologous chromosomes in four

phases.

Meiosis II• Divides sister chromatids in four phases.• DNA is not replicated between Meiosis I and

Meiosis II.

Mitosis Vs. Meiosis

Mitosis• One cell division• Homologous chromosomes

do not pair up• Results in diploid cells• Daughter cells are identical

to parent cell

Meiosis• Two cell divisions• Homologous chromosomes

pair up (Metaphase I)• Results in haploid cells• Daughter cells are unique

Sexual reproduction creates unique combinations of genes.• Fertilization

– Random– Increases unique combinations of genes– In humans, the chance of getting any one

combination of chromosomes from any one set of parents is one out of 223 x 223 (which is one out of over 64 trillion combinations)

Sexual reproduction creates unique combinations of genes.

• Independent assortment of chromosomes– Homologous chromosomes pair randomly along

the cell equator– Increases the number of unique combinations of

genes– In human cells, about 223 (8 million) different

combinations could result

Sexual reproduction creates unique combinations of genes.

• Crossing over– Exchange of chromosome segments between

homologous chromosomes– Increases genetic diversity– Occurs during Prophase I of Meiosis I– Results in new combinations of genes (chromosomes

have a combination of genes from each parent)

• There are 4 types of nucleotides: thymine, adenine, cytosine, and guanine• The nitrogen containing bases are the only difference in the four

nucleotides.

Proteins carry out the process of replication.

• DNA serves only as a template. • Enzymes and other proteins do the actual

work of replication.• Process

1. Enzymes unzip the double helix.2. Free-floating nucleotides form hydrogen bonds

with the template strand.nucleotide

The DNA molecule unzips in both directions.

3. DNA polymerase enzymes bond the nucleotides together to form the double helix.

3. DNA polymerase

4. new strand 2. Nitrogen bases

1. Sugar Phosphate Backbone

• DNA replication is semi-conservative, meaning one original strand and one new strand.

original strand new strand

Two molecules of DNA

4. Two new molecules of DNA are formed, each with an original strand and a newly formed strand.

• RNA differs from DNA in three major ways.

– DNA has a deoxyribose sugar, RNA has a ribose sugar.– RNA has uracil instead of thymine (found in DNA)

– A pairs with U– DNA is a double stranded molecule, RNA is single-stranded.

• 1. Transcription is catalyzed by RNA polymerase.

RNA polymerase and other proteins form a transcription complex. The transcription complex recognizes the start of a gene and unwinds a segment.

start site

5. nucleotides

transcription complex

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

6. RNA

Amino acids (protein building blocks) are coded for by mRNA base sequences.

• A codon is a sequence of three nucleotides that codes for an amino acid.

codon formethionine (Met)

codon forleucine (Leu)

• The genetic code matches each codon to its amino acid or function.

– three stop codons signal the end of a chain of amino acids.

– one start codon, codes for methionine and to start translation

The genetic code matches each RNA codon with its amino acid or function.

1. For translation to begin, tRNA binds to a start codon (Met in picture) and signals the ribosome to assemble.

– A complementary tRNA molecule binds to the exposed codon (Leu in picture), bringing its amino acid close to the first amino acid.

Some mutations affect a single gene, while others affect an entire chromosome.

A gene mutation affects a single gene. • Many kinds of mutations can occur, especially during

replication.Types of Gene Mutations:• A point mutation substitutes one nucleotide for

another. Ex: Sickle Cell Anemia

mutatedbase

Nonsense Mutation• Type of point mutation• Results in a premature stop codon

and usually a nonfunctional protein

• A frame-shift mutation inserts or deletes a nucleotide in the DNA sequence. Throws off the reading frame.

• THE CAT ATE THE RAT• THC ATA TET HER AT

• Chromosomal mutations affect many genes and an entire chromosome. Chromosomal mutations may occur during crossing over.

DeletionDue to breakageA piece of a chromosome is lost

InversionChromosome segment breaks offSegment flips around backwardsSegment reattaches

• Translocation results from the exchange of DNA (piece of one chromosome) segments between non-homologous chromosomes.

NondisjunctionFailure of chromosomes to separate

during meiosisCauses gamete to have too many or

too few chromosomes

Nondisjunction Can cause “Trisomy” (three copies of the same

chromosome in an egg or sperm)Trisomy 21 (Down syndrome)

• Gene duplication results from unequal exchange of segments crossing over. Results in one chromosome having 2 copies of some genes and the other chromosomes having no copies of those genes.

Several methods help map human chromosomes.

• A karyotype is a picture of all chromosomes in a cell.

X Y

9.1: Manipulating DNA

• Key Concept: – Biotechnology relies on cutting DNA at specific

places.

Restriction sites

A DNA fingerprint is a type of restriction map.

• DNA fingerprints are based on parts of an individual’s DNA that can be used for identification– Based on noncoding regions of DNA– Noncoding regions have repeating DNA sequences– Number of repeats differs between people– Banding pattern on a gel is a DNA fingerprint

DNA fingerprinting is used for identification.

• DNA fingerprinting depends on the probability of a match.– Many people have the same number of repeats in a

certain region of DNA– The probability that two people share identical numbers of

repeats in several locations is very small (only one chance in over 5 million people that they would match)

– Several regions of DNA are used to make a DNA fingerprint.

Uses of DNA Fingerprinting

• Evidence in criminal cases• Paternity tests• Immigration requests• Studying biodiversity• Tracking genetically modified crops

Cloning

• A clone is a genetically identical copy of a gene or an organism

• Cloning occurs in nature– Bacteria (binary fission)– Some plants (from roots)– Some simple animals (budding, regeneration)

Pros/Cons of Cloning

Benefits• Organs for transplant into

humans• Save endangered species• Reproduce beneficial traits

Concerns• Low success rate• Clones “imperfect” and less

healthy than original animal• Decreased biodiversity

Genetic Engineering• Involves changing an organism’s DNA to give it new traits• Based on the use of recombinant DNA

– Recombinant DNA contains DNA from more than one organism

(bacterial DNA)

Uses of Genetic Engineering

• Transgenic bacteria can be used to produce human proteins– Bacteria can be used to produce human insulin for diabetics

• Transgenic plants are common in agriculture– transgenic bacteria infect a plant– plant expresses foreign gene– many crops are now genetically modified

(GM)

• Transgenic animals are used to study diseases and gene functions

Documents

Module B Review