Chapter 4: Genes and Cellular Function

Merged flashcards from Chapter 4, McGraw Hill Anatomy and Physiology Ninth Edition, by Kenneth S. Saladin.

Heredity

The transmission of genetic characteristics from parent to offspring

Karyotype

The chart of all 46 chromosomes by sides; shows 23 pairs of homologous chromosomes

Homologous chromosomes

1 chromosome from each pair inherited from each parent

Autosomes

Chromosomes that look alike and carry the same genes

Sex chromosomes

Chromosomes that determine gender; men have one X and one Y chromosomes while women have homologous X chromosomes

Diploid

Any cell with 23 pairs of chromosomes; somatic (non-reproductive) cells are an example

Haploid

Cells with half as many chromosomes as somatic cells; human haploid cells contain 23 unpaired chromosomes such as sperm and egg cells to restore regular pairing

Locus

The location of a particular gene on a chromosome

Allele

Different form of a particular gene; the same alleles are found at the same locus on homologous chromosomes

Dominant allele

An allele that expresses a protein in an individual

Recessive allele

An allele that does not express in an individual if it is paired with a dominant allele; only appears when recessive on both homologous chromosomes

Genotype

The allele an individual possesses for a particular gene; visualized using Punnet square

Phenotype

An observable trait

Genetic counselors

Perform genetic testing and advise couples on genetic diseases

Gene pool

The genetic makeup of the whole population

Multiple alleles

More than two allelic forms of a gene; seen in A, B, and O blood types

Codominance

Both alleles equally dominant and phenotypically expressed; seen in AB blood types

Incomplete dominance

Heterozygous individual shows phenotype between traits each allele would have produced alone

Polygenic inheritance

Genes at two or more loci contribute to a single trait

Pleiotropy

One gene produces multiple phenotypic effects

Sex-linked traits

Traits carried on the X or Y chromosomes; men inherit more than the other due to having only one X chromosome

Penetrance of allele

Percentage of population exhibiting expected phenotype; allele may not fully express in population or can be modified by the environment

Epigenetics

Field examining nongenetic changes that alter gene expression and can be passed to offspring

Carcinogens

Environmental cancer-causing agents that can damage DNA; they can be found in radiation, chemicals, and viruses and cause uncontrolled cell growth

Law of Complementary Base Pairing

States that we can predict the base sequence of one DNA strand if we know the sequence of another

DNA replication steps

1. Unwinding

2. Unzipping

3. Building new strands

4. Repackaging

Replication fork

The point of DNA opening, this is made in step 1 after unwinding form histones

DNA helicase

The enzyme that unzips a segment of the DNA’s double helix structure in step 2

DNA polymerase

The enzyme that builds new DNA strands by matching free nucleotides to the unwinded DNA strand in step 3; the DNA is then repackaged and replicated for step 4

DNA Damage Response (DDR)

Mechanisms in place to correct replication errors by DNA polymerase; replaces unstable base pairs with correct pairs for a 1/1000000000 failure rate

Mutations

Changes in DNA structure due to replication errors or environmental factors; some may be harmless while others can cause defects or cancer later on

Cell cycle

The interphase and mitotic phases

Interphase

A part of the cell cycle that includes the first gap phase (G₁), synthesis phase (S), and second gap phase (G₂)

Mitotic phase

A part of the cell cycle that includes the prophase, metaphase, anaphase, telophase, and cytokinesis

First gap phase (G1)

Interval between cell birth and DNA replication; cell carries out normal tasks and accumulates materials for next phase

Synthesis phase (S)

Phase in interphase when the cell replicates all nuclear DNA and duplicates centrioles

Second gap phase (G2)

Interval between DNA replication and cell division; repairs errors and synthesizes enzymes

Mitotic phase

Phase where the cell replicates its nucleus

G zero phase (G0)

Cells that have left the cycle and ceased dividing for a long time

Mitosis

The cell division resulting in two genetically identical daughter cells; develops fertilized egg to 50 trillion cells and helps tissue growth

Phases of mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Prophase

First phase in mitosis where genetic material condenses into compact chromosomes; nuclear envelope disintegrates and centrioles sprout spindle fibers

Metaphase

Second phase in mitosis where chromosomes align on the cell equator; microtubules extend from side to middle

Anaphase

Third phase in mitosis where the spindle fibers cleave chromatids apart to opposite poles of cell

Telophase

Fourth phase where chromosomes cluster on each side of the cell; the rough ER makes a new nuclear envelope and the mitotic spindles disintegrate

Cytokinesis

Divison of the cytoplasm into two cells where the cell pinches in two; comes after telophase

Cell division factors

Starts when:

• Adequate cytoplasm

• DNA replicated

• Nutrients supplied

• Cell stimulated

May stop when:

• Neighboring cells

• Nutrients or growth factors withdrawn

Gene

An information-containing segment of DNA that codes for the production of RNA which in turn helps synthesize proteins

Genome

All the DNA in one 23 chromosome set

Genomics

The study of the whole genome

Genomic medicine

The application of knowledge of the genome to the prediction, diagnosis, and treatment of disease

Base triplet

Sequence of three DNA nucleotides that stand for one amino acid

Codon

A three base sequence in RNA

Start codon

Begins the amino acid sequence of the protein (AUG for methionine)

Stop codon

Ends the amino acid sequence like a period (UAG, UGA, and UAA)

Transcription

Copying the genetic instructions from DNA to mRNA

RNA polymerase

Binds to DNA and opens up the helix; reads bases from one strand of DNA to build a complementary strand of mRNA; then rebinds it

Pre-mRNA

Immature RNA produced by transcription

Exons

Segments of pre-mRNA exported from the nucleus and translated into protein which are spliced by enzymes

Introns

Segments of pre-mRNA that will be removed before translation

Messenger RNA (mRNA)

Carries code from the nucleus to cytoplasm and ribosome

Transfer RNA (tRNA)

Delivers a single amino acid to the ribosome; includes three nucleotides called an anti-codon to bind to mRNA and bring free amino acid using one ATP

Ribosome

Organelles that read mRNA and build peptide chains from amino acids; pulls mRNA through like a ribbon

Initation

Leader sequence in mRNA binds to a ribosomal subunit, joining the complex ribosome and allows for reading

Elongation

tRNA binds to the ribosome to pair with mRNA, brings amino acids to form a peptide bond

Termination

Releasing a protein and mRNA after reaching a stop codon; proteins may need to be packaged or exported

Chaperone proteins

Guides the folding of new proteins into secondary and tertiary structures; defends against heat or stress into correct shapes

Posttranslational modification

Proteins made on the ER are threaded into pores and enzymes to modify the protein through amino acid trimming, folding, and stabilization

Johann Miescher

A Swiss biochemist who lived from 1844 to 1895; he studied the nuclei of white blood cells and coined the term nuclein - what we now call genes

Deoxyribonucleic acid (DNA)

A long, thread-like molecule with uniform diameter and varied length; it’s a polymer of nucleotides

Nucleotide

A molecule made of a sugar, phosphate group, and nitrogenous base

Ribose

The sugar in nucleotides

Purines

The adenine and guanine nitrogenous bases

Pyrimidines

The cytosine, thymine, and uracil nitrogenous bases

Double helix

The structure of a DNA molecule; resembles a spiral staircase with the ‘steps’ being the nitrogenous base pairs

Base pairing

How DNA is bonded using hydrogen bonds; A always pairs to T with 2 bonds and C always pairs to G with 3 bonds

Gene

Segment of DNA coding for the synthesis of a specific protein

Genome

All the genes of one person; humans have 20,000 but only 2% is human-specific while the other 98% is for chromosome structure and gene activity regulation

Chromatin

Fine filamentous DNA material complexed with proteins; may change movement in non-dividing cells according to genetic activity

Ribonucleic acids (RNAs)

Contain the sugar ribose; uracil takes the place of thymine in DNA and is smaller

Messenger RNA (mRNA)

Sends the genetic code to ribosomes

Ribosomal RNA (rRNA)

Carries out protein synthesis in enzymes

Transfer RNA (tRNA)

Obtains amino acids for ribosomes according to mRNA