BIO 213 Babu Chapter 7-9

DNA structure and use

-Information storage in the nucleus

-Each molecule is a polymer made from 4 nucleotides: sugar, phosphate, and a nitrogenous base

Rosalind Franklin & Maurice Wilkins

used X-ray diffraction data to elucidate the structure of DNA

DNA Double Helix

Sugar phosphate backbones held together by H-bonding or "base pairing" between the bases

Complementary

One strand determines the sequence of the other

How is DNA read?

5' to 3'

Genome

all the genetic material in its cells, entire genetic complement

Genes and what they control

functional units on chromosomes, control protein production

Where are proteins synthesized?

Cytoplasm

RNA polymerase

synthesizes a copy of one gene from a DNA template as a heterogeneous nuclear RNA (hnRNA) molecule.

DNA vs. RNA

different sugars: DNA=T, RNA=U

DNA-stable, double stranded

RNA-unstable, single stranded

Direction of making RNA

Nucleotides are always made 5' to 3' so RNA is made 5' to 3' off of the 3' to 5' DNA template strand

Transcription steps

1. Initiation: RNA polymerase binds to DNA at the gene's promoter; the DNA helix unwinds; RNA synthesis begins

2. Elongation: hnRNA strand grows (5'-3')

3. Termination: RNA polymerase reaches the terminator and detaches the new hnRNA from the DNA

Bacteria cell transcription

-many genes are transcripted at once making a polycistronic RNA which codes for multiple proteins

-Genes and proteins colinear

RNA Processing

Newly synthesized RNA called heterogeneous nuclear RNA must be modified before it is fully functional as mRNA

-Caps are added

-tail is added (30-100 As long)

-Introns are removed via splicing

introns

non coding nucleotide sequences that are transcripted but not translated into proteins.

Exons

expressed sequence of DNA; codes for a protein; What is left after RNA procesing

2 types of RNA molecules used in translation

-Ribosomal RNA (rRNA) are a major component of the organelles (ribosomes) that construct proteins

-Transfer RNA (tRNA) read mRNA and insert amino acids to growing protein

The Genetic Code

The information to encode a single amino acid is carried in a sequence of three nucleotides

-Each triplet is called a codon

-The code is degenerate

-Some codons are STOP codons

-AUG start codon

Translation (& by what)

RNA translated into amino acids by ribosomes

4 stages of Translation

Initiation, Elongation, Translocation, Termination

Initiation (Translation)

small and large ribosomal subunits bind mRNA; first tRNA also binds; 1st 2 amino acids created

Elongation (Translation)

a peptide bond forms between the amino acid in the (P site) and the (A site)

Translocation (Translation)

ribosome ratchets over one codon jettisoning empty tRNA and accommodating another amino acyl tRNA; STEPS 2 & 3 REPEAT

Termination (Translation)

elongation ceases once a STOP codon is reached (UAA, UAG, or UGA)

Exit (E) site

tRNA exits after use

Peptidal (P) site

Grows amino acids for growing chain

Amino acyl tRNA (A) site

Site for next tRNA with amino acid to bind

Mutations

substitutions, insertions, or deletions of one or more nucleotides in a DNA molecule.

-can alter polypeptide folding causing genetic disorders.

Prion diseases

protein folded into an infectious conformation that is the cause of several disorders

Point/substitution mutation

One nucleotide is changed in the DNA strand, alters sequence but not total # in gene

Frameshift Mutation

Insertion or deletion of bases; can drastically affect mRNA translation

Cellular Division is essential to...

replace cells

asexual reproduction

Process by which a single parent reproduces by itself to create genetically identical offspirng

Sexual reproduction

A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents; each parent contributes a gamete

Fertilization

Fusion of an egg and sperm cell (gametes); grows zygote that will divide mitotically

Apoptosis

Programmed cell death

When does DNA replication happen and how

before mitosis and meiosis; Helicases unwind DNA, DNA polymerase copies DNA, Ligases seal up adjacent DNA molecules

Binary fission

How bacteria reproduce asexually, copy DNA and each cell gets 1 copy

Chromosomes

Where DNA is divided among, made of chromatin

Chromatin

Made of DNA+histone proteins called nuclesomes

When are chromosomes condensed

only right before replication and right after division

Diploid

Humans are diploid: 2 copies of each chromosome

Alleles

Different type of same gene. If a gene has the same alleles it is IDENTICAL

Cell cycle steps

events between division: Interphase, mitosis, cytokinesis

Interphase

Time between division for cell growth and DNA replication

-G1: RNA and proteins are made (46 chromosomes)

-S (synthesis): DNA is replicating

-G2: Preparing for cell division (46 pairs of chromosomes)

-G0: Cells Never divide

What is the longest portion of the cell cycle

Interphase

Mitosis

PPMAT, happens in somatic cells

-Prophase: Chromosomes condense into chromatids, nuclear envelope breaks down, spindle fibers from centrioles grab chromatids

-Prometaphase: Chromosomes are lining up, sister chromatids still held together by centromere

-Metaphase: Chromosomes are lined up in middle/spindle equator

-Anaphase: Chromosomes divide and each sister chromatid turns into a chromosome

-Telophase: Chromosomes reach each end. decondense, nuclear envelop reforms, cells begin to take shape

Cyotokinesis

Cytoplasm divides to yield 2 daughter cells that are genetically identical and diploid

Meiosis

Happens in germ cells; Yields 4 haploid cells, undergoes replication them PPMAT x2

Gametes

A haploid cell such as an egg or sperm, has one copy of each chromosome

Homologous Pairs

A pair of chromosomes of the same type, one from each parent. May have different alleles

What steps in meiosis increase genetic diversity

Homologous recombination mixed DNA, and indpendent assortment (when pairs line up in metaphase I their order is random)

At what points in the cell cycle are sister chromatids separated from one another

Anaphase (mitosis) and Anaphase II (meiosis)

Polyploidy

condition in which an organism has extra sets of chromosomes

Nondisjunction events

Gametes with 1 extra or missing chromosome (down, triplo X, Klinefelter, Jacobs, and turner syndrome

Steps from DNA to protein (flow of information)

Central Dogma of molecular biology

1) RNA polymerase (transcription) -> hnRNA

2) RNA processing -> mRNA

3) Translation -> protein