Bio unit 3

What is the most common point of control for gene expression

• Transcription initiation

  • Cells usually regulate whether RNA polymerase can begin transcribing a gene into mRNA

Why is transcription initiation an efficient control point

• It prevents unnecessary production of mRNA proteins, saving energy and resources for the cell

What is positive control of transcription

• activator increases transcription by helping RNA polymerase to bind to DNA or begin transcription

What is a negative control transcription

• Repressor decreases transcription by blocking RNA polymerase from transcribong a gene

What is an activator protein

• a regulatory protein that binds DNA and increases transcription

What is a repressor protein

• a regulatory protein that binds DNA and decreases transcription

How do activators help RNA polymerase

• They make it easier for RNA polymerase to bind to the promoter and start transcription

How do repressors prevent transcription

• they bind to regulator regions (often operators) and block RNA polymerase

What is induction

• Occurs when transcription is normally OFF and becomes ON when an inducer molecule is present

  • ex. lactose in lac operon

What is repression

• Occurs when transcription is normally ON and becomes OFF when a repressor is activated

  • ex. Tryptoohan in the TRP operon

Which operon is inducible

• lac operon

Which operon is repressible

• trp operon

How is gene regulation different is prokaryotes

• simpler regulation

• genes often organized into operons

• transcription and translation occur simultaneously

How is gene regulation different in eukaryotes

• more complex regulation

• DNA wrapped around histones

• transcription separated from translation

• multiple levels off controls

Do eukaryotes have operons

• no they are regulated individually

Why is gene regulation more complex in eukarytotes

• DNA must be accessible through chromatin remodeling, and regulation occurs at transcriptional, post-transcriptional, translational, and post-translational levels

What is chromatin

• DNA wrapped around histone proteins

How does tightly packed chromatin affect gene expression

• reduces gene expression because transcription factors and RNA polymerase cannot easily access DNA

How does loosely packed chromatin affect gene expression

• promotes gene expression because DNA is accessible

What does histone acetylation do

• loosens chromatin structure and generally increases transcription

What is DNA methylation associated with

• reduced transcription and gene silencing

What is post-transcriptional regulation

• occurs after mRNA is made but before protein is produced

What role does alternative RNA splicing play

• different combinations of exons can be joined to produce multiple proteins from a single gene

How does mRNA stability affect gene expression

• Long-lived mRNAs can be translated many times, increasing protein production

• Short-lived mRNA decrease protein production

How does mRNA transport regulate gene expression

• only mRNAs that leave the nucleus can be translated

How can translation be regulated

• proteins and RNAs can increase or block ribosome attachment to mRNA

What are small RNAs

• short RNA molecules that regulate gene expression after transcription

What are microRNAs (miRNA)

• small RNAs that bind complementary mRNA sequences and block translation or promote mRNA degradation

What are small interfering RNAs (siRNAs)

• small RNAs that target specific mRNAs for destruction through RNA interference (RNAi)

What is RNA interference (RNAi)

• a mechanism in which small RNAs help silence gene expression by destroying mRNA or preventing its translation

How are unwanted proteins marked for destruction

• they are tagged with ubiquitin molecules

What is ubiquitin

• a small protein that acts as a “destroy me” signal for cellular proteins

What is the proteasome

• a large protein complex that recognizes ubiquitin-tagged proteins degrades them

Why is protein degradation important

• removes damaged proteins

• controls protein levels

• helps regulate cellular processes

• prevents accumulation of unnecessary proteins

What is binary fission

• asexual reproduction used by prokaryotes in which a single cell replicates its DNA and divides into two genetically identical cells

What is mitosis

• a process of nuclear division in eukaryotic cells that produces two genetically identical daughter nuclei

Which types of cells use binary fission

• prokaryotic cells (bacteria and archaea)

What type of cell uses mitosis

• eukaryotic cells (animals and plants)

How are binary fission and mitosis similar

• both produce genetically identical daughter cells and ensure Dna is passed to offspring

How are binary fission and mitosis different

• binary fission is simpler and occurs without a nucleus while mitosis involved chromosomes within a nucleus and a spindle apparatus

What is a chromosome

• a structure containing DNA and assoiated proteins that carries genetic info

What protein is primarily responsible for packaging DNA in eukaryotes

• histone proteins

What is a nuclesome

• DNA wrapped around a group of histone proteins

Why is DNA packaged into chromosomes

• to fit inside the nucleus and protect the gentic info

What is chromatin

• the DNA protein complex that make up chromosomes

How does chromatin change before cell divison

• it condenses into visible chromosomes

What are sister chromatids

• two identical copies of a replicated chromosome joined together

What is a centromere

• the region where sister chromatids are attached

What are two major stages of the cell cycle

• interphase and M phase

What are the three stages of interphase

• G1, S, and G2

What happens during G1

• cell growth and normal metabolic function occur

What happens during S phase

• DNA reeplication

What happens during G2

• the cell grows further and prepares for divison

What happens during M phase

• Mitosis and cytokinesis occur

What is the correct order of the cell cycle

• G1 → S → G2 → M

What occurs during interphase

• the cell grows, performs normal function, replicates DNA, and prepares for divison

What occurs in M phase

• the nucleus divides (mitosis) and the cell splits (cytokinesis)

What happens during prophase

• Chromosomes condense, spindle fibers begin forming, and the nuclear envelope starts to break down

What happens during prometaphase

• the nuclear envelope disappears and spindle fibers attach to chromosomes

What happens during metaphase

• Chromosomes align at the cells equator

What happens during anaphase

• sister chromatids separate and move towards opposite poles

What happens during telophase

• new nuclei form around each set pf chromosomes

What is cytokinesis

• division of the cytoplasm to form two daughter cells

What is a cell cycle checkpoint

• a control point where the cell assesses whether it can safely proceed to the next stage

Why are check points important

• they help prevent damaged or incomplete DNA from being passed to daughter cells

What is the G1 check points

• determine whether conditions are favorable for DNA replication

  • Nutrients?

  • cell size?

  • growth factors?Wh

What is the G2 checkpoints

• verifies DNA replication was completed correctly before mitosis

  • replication complete?

  • DNA damage?

What is the spindle checkpoint

• ensures chromosomes are properly attached to spindle fibers before separation

What happens if a cell fails a checkpoint

• the cycle may stop for repair or the cell may undergo programmed cell death (apoptosis)

What is proto-oncogene

• a normal gene that promotes cell growth and divsion

what is oncogene

• a mutated proto oncogene that drives excessive cell division

What is a tumor suppressor gene

• normally slows cell division or triggers DNA repair

How can checkpoint failure cause cancer

• damaged cells continue dividing instead of being repaired or destroyed

How does mutation of tumor suppressor gene promate cancer

• the cell loses important growth control mechanism

What is metastasis

• the spread of cancer cells from the original tumor to the other parts of the body

What is meiosis

• a type of cell division that produces haploid gametes (sperm and egg cells) from diploid parent cells

What is the role of meiosis in sexual reproduction

• reduces the chromosomes number by half so fertilization can restore the normal diploid number

What are gametes

• haploid reproductive cells such as sperm and eggs

What does haploid (n) mean

• having one set of chromosomes

What does diploid (2n) mean

• having two sets of chromosomes

Why is meiosis necessary for sexual reproduction

• without it, chromosome numbers would double every generation

How does meiosis contribute to genetic diversity

• through crossing over and independent assortment of chromosomes

What is snyapsis

• the pairing of homologous chromosomes during prophase 1

What are homologous chromosomes

• chromosome pairs that carry the same genes but may have differnt alleles

Why is synapsis important

• it allows homologous chromosomes to exchange genetic material during crossing over

What is crossing over

• the exchange of DNA between homologous chromosomes

During which phase does crossing over occur

• prophase 1 of meiosis

What is the result of crossing over

• recombinant chromosomes with new combinations of alleles

Why is crossing over important

• it increases genetic variation among offspring

What is reductive division

• reduces chromosomes number from diploid 2n to haploid n

During which meiotic division does reductive division occur

• Meiosis 1

WHy is reductive division important

• is ensures that gametes contain only one set of chromosomes

What happens during prophase 1

• chromosomes condense, homologous chromosomes pair through synapsis, and crossing over occurs

What happens during metaphase 1

• homologous chromosomes pairs line up at the middle of the cell

What happens during Anaphase 1

• homologous chromosomes separate and move to opposite poles

What happens during telophase 1

• chromosomes reach opposite poles and the cell divides

What is the outcome of meiosis 1

• two haploid cells duplicated chromosomes

What happens during prophase II

• chromosomes condense and new spindle forms

What happens during metaphase II

• chromosomes line up individually along the metaphase plate

WHat happens during anaphase II

• sister chromatids separate and move to opposite poles