Biology Exam 3

DNA stores

genetic material

______ encodes the information to make polypeptides and RNA molecules

DNA (1)

________ is packaged in chromosomes and stored in the __________

DNA; nucleus

DNA ------> mRNA

transcription

mRNA------>protein

translation

The 5 levels of organization in DNA structure are

1. nucleotides, 2. single strand, 3. double helix, 4. chromosome, 5. genome

Chromosomes are composed of

chromatin

chromatin

DNA wound around histone proteins

Humans have how many chromosomes?

46 (23 pairs)

DNA nucleotide

phosphate group, sugar (deoxyribose), base

What are the bases of DNA?

Adenine, Thymine, Guanine, Cytosine

RNA nucleotides

phosphate group, sugar (ribose), base

What are the RNA bases?

Adenine, Uracil, Cytosine, Guanine

Nucleotide numbering system

Sugar carbons are 1' to 5' Hydroxyl group (-OH) attached to 3' carbon on sugar Phosphate attached to 5' carbon on sugar Base attached to 1' on carbon sugar

single strand

phosphodiester bonds link nucleotides forms sugar-phosphate backbone bases project away from backbone has directionality-5' to 3'

In a nucleotide single strand

sugars and phosphates alternate 5' has free phosphate group 3' has free sugar group

double helix

-double stranded helix -strands run antiparallel -bases project toward the center

complementary base pairing rules

A always pairs with T G always pairs with C

purines

Adenine and Guanine

Pyrimidines

Cytosine and Thymine

more characteristics of the double helix

-uses base pairing rules -antiparallel strands (3' to 5' with 5' to 3')

Chromosomes

consists of chromatin which is highly compacted DNA wrapped around histone proteins

To compact DNA and package into chromosomes:

1. double helix is wound into nucleosomes 2. nucleosomes to chromatin 3. 30 nm fiber 4. radial loop domain 5. compacted radial loop domain

2 broad forms of chromatin

euchromatin (less compacted DNA, active genes) and heterochromatin (highly compacted DNA, inactive genes)

genome

all of an organism's genetic material

autosomal chromosomes

non-sex chromosomes 22 pairs in humans

sex chromosomes

Chromosomes that determine the sex of an individual 1 pair in humans

DNA replication

the process of making a copy of DNA for cell division

gamete production, cell renewal/growth, embryogenesis

DNA replication

DNA replication follows the __________ rule

AT/GC

during DNA replication

parental/original strands sperate and serve as template for the synthesis of a new/daughter strand

True or False: DNA replication is semi-conservative

True

Replication proceeds in _______ directions from an ________________________

both; origin of replication

origin of replication

Site where the replication of a DNA molecule begins.

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

steps of the formation and movement of the replication fork

1. DNA helicase unwinds DNA at replication fork 2. Single-strand binding proteins bound to prevent reforming double helix 3. DNA topoisomerase prevents tangling of DNA ahead of replication fork 4. DNA polymerase links nucleotides together to form DNA strands

DNA polymerase

Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule

DNA polymerase adds nucleotides to which prime end?

3'

A ______ primer is needed to start DNA replication

RNA

DNA primase

synthesizes short RNA primers

DNA replication process

On a strand 3' to 5': 1. RNA primer is laid down 2. leading strand of DNA is laid down to the replication fork From replication fork to origin (5' to 3') 1. RNA primer laid in front of origin of replication 2. Okazaki fragment is laid down from end to origin 3. process repeats to create the lagging strand

leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction toward replication fork

lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.

Okazaki fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.

True or False: The RNA primer can stay in the lagging strand.

FALSE: it must be replaced with DNA nucleotide AKA DNA polymerase

DNA ligase

Seals gaps between Okazaki fragments

True or False: DNA replication is very accurate

True, DNA polymerase has a proofreading mechanism to check for errors.

To fill in the 3' ends of the DNA strands, ___________ must be attached to the ends

telomeres

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes. -prevent loss of genetic material -added by enzyme telomerase -as we grow, telomeres are shortened

Genome

the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes

Proteome

the entire set of proteins expressed by a given cell or group of cells

Gene

segment of DNA that encodes a functional product -can encode polypeptides or functional RNA molecules

gene expression

1. DNA stores info in genes 2. Transcription of DNA to produce RNA copy of gene 3. mRNA, the copy of gene that will be used to make polypeptide 4. Translation produces polypeptide using mRNA

DNA to RNA to polypeptide

gene expression (transcription and translation)

Where does the gene expression processes take place?

Prokaryotic- cytosol and ribosomes Eukaryotic-takes place in nucleus and ribosomes (either free or ones attached on Rough ER)

Transcription

synthesis of an RNA molecule from a DNA template

mRNA is complementary to

template strand (NONCODING STRAND)

mRNA sequence is the same as

non-template strand (CODING STRAND)

structure of a gene

promoter, regulatory sequence, terminator, transcribed region

Briefly describe the promoter, regulatory sequence, terminator, and transcribed region of a gene

promoter-START of transcription; place where RNA polymerase binds regulatory sequence-transcription factors (regulatory proteins) bind and control the rate of transcription terminator-END of transcription transcribed region-contains info that specifies an amino acid sequence; MIDDLE of gene

What are the three stages of transcription?

initiation, elongation, termination

Transcription initiation

sigma factor recognizes promoter and recruits RNA polymerase; DNA is unwound to separate strands; sigma factor released and RNA polymerase proceeds down DNA

Transcription Elongation

RNA polymerase continues down DNA strand using the template strand to make complementary RNA

Transcription Termination

When RNA polymerase reaches terminator, transcription stops & RNA chain is released

RNA processing in eukaryotes

-addition of 5' cap -addition of polyA tail -splicing AKA (Capping, Splicing, and tailing)

RNA splicing

Process by which the introns are removed from RNA transcripts and the remaining exons are joined together. (exons-expressed regions) (introns-intervening regions) -alternative splicing allows different proteins to be produced from the same gene

Organization of mRNA

ribosomal binding site-ribosome binding site, start codon-first amino acid, coding sequence-interchanging codons, stop codon-specifies stop

Codons

The three-base sequence of nucleotides in mRNA that specify a particular amino acid

The ______________ specifies amino acids within polypeptide

genetic code

The genetic code is _________________.

degenerate (same amino acid can be used repetitively)

tRNA contains what type of codon?

anticodon

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon -carries amino acid specified by codon (tRNA)

AUG

start codon

UGA, UAA, UAG

stop codons

Where does translation occur?

ribosome

Characteristics of ribosomes

two subunits- Large and Small subunits composed of rRNA and proteins 3 sites where tRNA binds during translation: A, P, and E sites

________________ alter DNA sequence of a gene

Gene Mutation

Mutation

A change in a gene or chromosome. -heritable change -source of variation for natural selection -most are harmful -genetically inherited diseases result from harmful mutations

point mutation

gene mutation in which a single base pair in DNA has been changed -caused by base substitution

Three types of point mutations

silent, missense, nonsense

silent mutation

A mutation that changes a single nucleotide, but does not change the amino acid created. -causes no change in protein structure or function

missense mutation

A base-pair substitution that results in a codon that codes for a different amino acid. -may change protein structure/function or may not -usually neutral or negative outcome

nonsense mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. -usually negative outcome

indel mutation (base insertion or deletion)

a mutation in which one or more nucleotide pairs is added or deleted -may cause change in reading frame -addition or deletion shifts the reading frame and changes codons and resulting amino acids

frameshift mutation

mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide -changes amino acid sequence -negative outcome; changes protein structure/function

mutations can also occur in _______________ regions

regulatory; may alter gene expression

Mutations occur in these type of cells:

germline and somatic

germline mutation

DNA alteration occurring in gametes that can be transmitted to offspring

somatic cell mutation

change within cells of the body, cannot be transmitted

spontaneous mutations

random change in the DNA due to errors in replication that occur without known cause

induced mutations

caused by environmental agents -chemical agents (cigarrete smoke or asbestos) -physical agents (UV light or X rays)

Cancer

caused by accumulation of mutations that eventually cause excessive cell proliferation (rapid cell division) -around 7-10 mutations

progression of cancer

1. initial tumor cells- accumulate mutations that increase cell division 2. benign tumor-overgrowth of normal cells 3.malignant tumor-overgrowth of abnormal (cancerous) cells 4.metastasis-malignat cells enter bloodstream or lymphatics and spread throughout the body

Mutations in these cells promote cancer

proto-oncogenes and tumor suppressor cells

Apoptosis

programmed cell death

Proto-oncogenes

promote normal cell division and growth -become oncogenes when develop gain-of-function mutation

Oncogenes

overactive, abnormal genes that promote excessive cell division and prevent apoptosis

Normal signaling pathway that promotes cell division

1. growth factor signal binds to a receptor, leading to receptor activation 2. signal transduction pathway 3. proteins/transcription factors are activated that promote transcription of genes involved in cell division ONCOGENES AFFECT ANY OF THESE AREAS

tumor suppressor genes

genes who's loss of activity promotes excessive cell division -encode proteins that normally prevent cell division, promote apoptosis, and involved in DNA repair

p53

tumor suppressor gene mutated in 50% of cancers -if DNA is damaged, p53 prevents cell division -if DNA is repaired, p53 cell divides normally -if DNA is not repaired, p53 promotes apoptosis

Chromosomes are inherited in ________ and occur as _________________ pairs

sets; homologous

homologous chromosomes

pair of chromosomes of the same type

diploid cells have ____ sets of chromosomes

two

haploid cells have ____ set of chromosomes

one (gametes)

cell cycle

series of events that cells go through as they grow and divide

Phases of the cell cycle

1. Interphase (G1, S, G2) 2. Mitosis (PMAT) 3. Cytokinesis (cell division)

Mitosis

part of eukaryotic cell division during which the cell nucleus divides -parent cell divides to produce 2 genetically identical daughter cells

S phase of cell cycle

chromosomes are replicated to produce a pair of sister chromatids

Steps of S phase

1. before mitosis, chromosomes replicate to make a pair of sister chromatids 2. chromosomes compact at beginning of mitosis

makeup of chromatin

held together by centromere kinetochore is the place where spindle fibers attach (near centromere)

Chromosomes vs chromatids

Chromosomes are made up of a pair of chromatids, while chromatids are two strands of a chromosome that divide during cell division.

spindle apparatus

responsible for organizing and sorting chromosomes during cell division -spindle fibers are microtubules of cytoskeleton that attach at kinetochore.

Stages of Mitosis

1. Prophase 2. Metaphase 3. Anaphase 4. Telophase/Cytokinesis

Interphase

G1, S, and G2; all DNA is replicated

Prophase

Chromosomes become visible and condense, nuclear envelop dissolves, spindle forms

Prometaphase

chromatids attach to the spindle; nuclear envelope has completely broken down

Metaphase

Chromosomes line up (end to end) in the middle of the cell on metaphase plate

Anaphase

sister chromatids move to opposite ends of the cell

Telophase and Cytokinesis

Nucleus reforms (telophase) and cell is divided in two (cytokinesis) -splits by cleavage furrow

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms -produces 4 haploid gametes -Phases: Interphase, Meiosis 1 and Meiosis 2

Characteristics of phases of meiosis

Interphase: chromosomes duplicate Meiosis 1: homologous chromosomes separate Meiosis 2: sister chromatids separate

Differences between mitosis and meiosis

-Meiosis has 2 divisions; Mitosis has 1 division -Meiosis makes haploids; Mitosis makes diploids -Meiosis makes 4 cells; Mitosis makes 2 -Meiosis makes gametes; Mitosis makes somatic -Meiosis makes genetically different daughter cells; Mitosis makes identical daughter cells

Stages of Meiosis 1

Prophase 1, Prometaphase 1, Metaphase 1, Anaphase 1, Telophase/Cytokinesis 1 -play same roles as mitosis phases, except they use bivalents and crossing over. -during this metaphase, chromosomes line up side by side -results in 2 haploid cells

Stages of Meiosis 2

Prophase 2, Prometaphase 2, Metaphase 2, Anaphase 2, Telophase/Cytokinesis 2 -same roles as mitosis -results in 4 haploid cells

Gametogenesis

production of gametes (spermatogenesis and oogenesis)

Spermatogenesis

Formation of sperm -begins at sexual maturity -produces 4 functional gametes 1. spermatogonia, 2.primary spermatocyte, 3.secondary spermatocyte, 4.spermatids, 5.sperm cells

Oogenesis

Egg production -starts at fetal development -born with primary oocytes in prophase 1 -each month, 1 primary oocyte continues with meiosis -gives rise to only 1 functional gamete 1. oogonia, 2.primary oocyte, 3.secondary oocyte, 4. ovum, 5. polar bodies

Variations in Chromosome Number

euploids, polyploids, and aneuploids

Euploid

chromosomes occur in complete sets EX) haploids have 1 set and Diploids have 2 sets

Polyploid

3 or more sets of chromosomes EX) triploids-3, and tetraploid-4

Aneuploid

Abnormal number of chromosomes. EX) trisomy-extra copy and monosomy-missing copy -conditions result from chromosomes not separating properly; most are not compatible with life -occurs in sex chromosomes too and usually have better quality of life

Aneuploidy results from

nondisjunction

Nondisjunction

chromosomes do not separate properly during cell division

Chromosome numbers are _________ between species, but _________ within species

different; same EX) Humans 23 pairs but Dogs have 39

Mendel's Laws of Inheritance

law of equal segregation and law of independent assortment

Gregor Mendel

Father of genetics -pea plant experiments investigated inheritance -it was believed all lines were true breeding (pure bred) -experiments showed law of segregation and law of independent assortment -3:1 ratio

law of equal segregation

a gene has two copies and during gamete production the gene copies separate equally

Characteristics of Mendel's law of equal segregation

1. an individual carries 2 alleles for a given character 2. traits exist in 2 forms: dominant and recessive 3. alleles segregate equally during gamete formation and each gamete receives 1 allele 4. 1 male gamete and 1 female gamete randomly combine during fertilization

The chromosomal basis of equal allele segregation

1. Chromosomes replicate, and cell progresses to metaphase of meiosis I. 2. Homologs segregate into separate cells during meiosis I. 3. Sister chromatids separate during meiosis II to produce 4 haploid cells.

Genotype

genetic makeup of an organism -homozygous-2 identical alleles -heterozygos-2 different alleles

Allele that is most common in nature is the

wild/normal type

Allele that does not occur commonly in nature is the

mutant/affected type

Phenotype

observable characteristics of an organism

_____________ is a tool used to predict the outcome of genetic crosses

punnet square

Probability

the chance of a particular outcome in genetics -number of times the outcome could occur

law of independent assortment

alleles of different genes assort independently during gamete formation

the chromosomal basis of independent assortment

Alignment of homologs can occur in more than one way during metaphase 1 (shown in picture)

Simple single gene inheritance in humans

Most genetic traits in humans are determined by interactions between several genes or between genes and the environment Traits include: genetically inherited disorders (cystic fibrosis etc.), ABO blood groups, color vision vs colorblindness

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family. -circles females, squares males, colored affected by trait, open unaffected by trait

autosomal recessive traits

traits that are only displayed if you have two copies of the recessive allele of a gene -affected ex: bb -unaffected ex: Bb or BB usually have unaffected parents

autosomal dominant traits

Affected individuals have at least one affected dominant allele -affected ex: BB or Bb -unaffected ex: bb usually has an affected parent

Tay Sachs and Cystic fibrosis

autosomal recessive traits

Dwarfism and Huntington disease

autosomal dominant traits

Determining gender

-Males XY, Females XX

X linked recessive traits

-occur more often in males -males have heterozygous mothers -affected females MUST have affected FATHER EX color blindness