HUMB C12

Nucleic acids

In all cells and viruses

Organic macromolecules (C,H,O,N,P)

Made of polynucleotides (chain of repeating nucleotide monomers)

Sequence of nitrogenous bases carries information

Two major classes: Deoxyribonucleic Acid (DNA), Ribonucleic Acid (RNA)

nucleotide

each contain:

A pentose sugar – deoxyribose, ribose

A phosphate group

A nitrogenous base – adenine, guanine, cytosine, thymine, uracil

Nucleoside

pentose sugar + nitrogenous base

Deoxyribonucleic Acid (DNA)

Mainly in nucleus, but also in mitochondria

codes protein synthesis

carries information for hereditary characteristics

1.5% of DNA encodes the 20,000 – 25, 000 genes in human genome

98.5% of DNA is non-coding (regulatory sequences, introns, repeat elements)

DNA structure

Double helix model - two antiparallel polynucleotide chains with an alternating deoxyribose-phosphate backbone

Complementary nitrogenous bases held together by weak hydrogen bonds form rungs of the ladder, adenine pairs with thymine and guanine pairs with cytosine

Organisation of DNA

DNA wrapped around proteins called histones to form chromatin

Chromatin twists and condenses to form chromosomes, each with hundreds to thousands of genes

Quantity of DNA

Each somatic (not sperm or egg) human cell nucleus has two copies of each chromosome (diploid) – one inherited from mother, other from father (homologous pair)

Each somatic cell has 46 chromosomes (23 pairs), 22 pairs are autosomal and 1 pair of sex chromosomes (women = XX, men = XY)

gametes (sperm or eggs) only have 1 chromosome of each homologous pair, so 23 haploid chromosomes

karyotype

image that arranges chromosones next to their pair during metaphase

Ribonucleic acid (RNA)

Single stranded polymer wuth an alternating ribose-phosphate backbone

Self complementary sequences forms folds, bulges, and helices

Supports DNA during protein synthesis

Found in nucleus and cytoplasm

Nitrogenous bases: adenine pairs with uracil, guanine pairs with cytosine

Types: mRNA, tRNA, rRNA

Different types have different sizes, shapes and functions

mRNA

m = messenger

transcription: carries information from DNA to ribosomes

tRNA

t = transfer

translation: brings amino acids to ribosomes

rRNA

r = ribosomal

integral part of ribosomes for protein synthesis

Genes and alleles

segment of DNA that codes for a protein

homologus chromosomes have genes in same locations but the allele (alternative form of a gene) can be different

Dominant and recessive alleles

Dominant alleles express themself even if only one copy is present, capital

Recessive alleles can only express themself if both copies are present, lowercase

eg is A = blue, Aa = blue

Genotype and Phenotype

Genotype – the actual gene (AA, Aa, aa)

Phenotype - person’s appearance (blue eyes, brown hair)

Sex-linked traits

affected by genes on sex chromosomes

if on X chromosome they appear in males and females

if on Y chromosome they only appear in males

Proteins

Organic macromolecule containing mainly C, H, O, and N

Long chain of amino acids linked by peptide bonds

Dipeptide (2 aa), oligopeptide (3-10 aa), polypeptide (10+ aa), protein (50+ aa)

Each amino acid has an amine group, acarboxyl group, a hydrogen atom, and a distinguishing side chain

Humans have 20 amino acids - 9 essential, 5 non-essential, 6 conditional (not essential but needed during illness/stress)

Protein Functions

function depends on protein’s ability to bond with other molecules

enzymes regulate metabolic processes, hormones regulate physiological processes

hemoglobin transports gases in blood, plasma proteins transport many substances in blood, protein channels in cell membrane control movement of substances in and out of cells

antibodies protect against foreign substances

allow muscle contraction

collagen fibres for structural frameworks, keratin strengthens skin, hair, and nails

can be broken down for energy

form cilia to move substances across cell surface and flagella to move sperm

Recommended intake of proteins

10-35% of total calories

Protein structure

Primary - Sequence of amino acids linked by peptide bonds

Secondary - folding into alpha helices or beta pleated sheets

Tertiary - 3D shape formed by alpha helices and beta pleated sheets folding

Quaternary - combined 3D structure of 2 or more polypeptide chains

Protein Types

Fibrous: elongated polypeptide chains arranged in parallel along one axis, insoluble, chemically stable, structural (support and strength), less sensitive to changes in temperature, pH

Globular: polypeptide chain compactly folded into rounded shape, water soluble, chemically active, functional (aid biological processes), sensitive to changes in temperature, pH

proteome

Proteome of a cell is all the proteins that a cell makes

Different cells make different proteins for exportation or cell functions

Cell’s DNA contains instructions for protein synthesis

Genetic code

specific arrangement of nucleotides in DNA and RNA that determine a protein’s amino acid sequence

Gene expression

production of proteins from the information stored in DNA

2 steps: transcription and translation

Central dogma

directional flow of information from DNA to RNA to Protein

Transcription

one polynucleotide chain named ‘coding strand’ and the other ‘template strand’

Initated by transcription factors that recruit RNA polymerase

Starts at promoter region, ends at terminator sequence

DNA uncoils and unzips, RNA polymerase attaches to template strand and copies genetic information to form mRNA with complimentary base pairing, mRNA exits nucleus through nuclear pores

Codons & amino acids

codon: sequence of 3 nitrogenous bases on mRNA, read by a ribosome

64 possible codons, but only 20 amino acids

an amino acid is specified by 1-6 codons

degenerate code - some codons have the same meaning

AUG is start codon

UAG, UAA, UGA are stop codons

tRNA

contains three nitrogeous bases (anticodon) and an amino acid specified by the correlating codon on the mRNA

Translation

mRNA goes to ribosomes

Ribosome reads one codon (3 nitrogenous bases) at a time

A tRNA with the amino acid specified by the codon and with a matching anticodon binds to codon

Amino acids linked by peptide bonds

empty tRNA detatches from ribosome and returns to cytoplasm to be reloaded with a new amino acids

Post-translational modification

After translation

Other functional groups can be attached, aa can be cleaved off the end, polypeptide can be cut in half, protein can be activated

Changes or extends protein’s function

Locus

location of a gene on a chromosome

Cell Types

Somatic - form body of multicellular organism, most cells, 46 chromosomes (diploid number), mitosis

Germ - give rise to gametes, located in gonads (ovaries + testes), meiosis

Gamete - fuse during sexual reproduction, sperm or egg, 23 chromosomes (haploid number)

Centromere

pernament DNA region that joins two sister chromatids after replication and site of spindle fibres

Centrioles & Spindle Fibers

2 centrioles located in centrosome

Before cell division, centrioles divide, move to ends of cell, and organize spindle fibers

Cell Life Cycle

Interphase: phase between cell division, divided into G1 phase, S phase, and G2 phase

Mitosis: 1 mother cell divides into 2 genetically identical somatic daughter cells, divided into prophase, metaphase, anaphase, and telophase

Cytokinesis

Interphase

DNA is unwound chromatin

G1 phase - routine metabolism

S phase - DNA replicated, each chromosome becomes two sister chromatids joined at a centromere

G2 phase - mitosis preparation, organelles replicated

Mitosis

Prophase: chromatin condenses making chromsomes visible, centrioles migrate to ends of each cell, spindle fibres attach to centromeres, nuclear envelope disintegrates

Metaphase: chromosomes align at the nuclear equator

Anaphase: spindle fibres separate the chromatids (each chromatid now referred to as a chromosome), 2 identical sets of chromosomes are moved to separate ends of the cell, cytokinesis begins

Telophase: nuclear envelope reforms around each set of chromosomes, chromosomes decondense into chromatin, cytokinesis continues

Cytokinesis

mother cell’s cytoplasm divides into 2 genetically identical somatic daughter cells

Mitosis examples

Areas of high abrasion (oral cavity, female reproductive tract)

Skin - Constant mitosis in basal layer, cells grow up superficially to replace top layer of cells

brain, heart, skeletal muscle has slow mitosis

Meiosis

Less common - Specialized for sexual reproduction

1 round of DNA replication followed by 2 cell divisions

In the gonads (testes/ovaries), 1 germ cell divides to produce 4 genetically different, haploid (23 chromosomes) gametes (sperm/egg)

Gametes unite, forming a zygote (new, genetically unique human being)

Meiosis 1 - Prophase 1

DNA replication already occured - nucleus has 46 chromosomes (23 pairs) each with two sister chromatids joined by a centromere

Prophase 1 - homologous crossing over: homologous chromosomes synapse (pair up - 1 paternal and 1 maternal chromosome) to form a tetrad (4 chromatids), non-sister chromatids of the homologous pair exchange matching segments of DNA so that sister chromatids are no longer identical, allowing new gene combinations from

Meiosis 1 - Metaphase 1

Homologus chromosome pairs line up at cell’s centre with random maternal/paternal orientation (increasing possible gene combinations)

Meiosis 1 - Anaphase 1

Whole chromosomes (with 2 sister chromatids still joined by centromere) move to opposite sides of cell

Meiosis 1 - Telophase 1

2 new non-identical cells form, each with 23 chromosomes with replicated DNA (each chromosome made of 2 sister chromatids joined at a centromere)

Meiosis 2

There is no DNA replication

Both cells from meiosis 1 undergo Prophase, Metaphase, Anaphase, and Telophase the same as mitosis

Results in 4 genetically unique haploid cells, each with 23 chromosomes made of a single chromatid

Spermatogenesis vs Oogenesis

Oogensis:

1 functional oocyte and 3 nonfunctional polar bodies per meiotic cycle

At birth, ovaries contain all the oocytes they will ever have, they are stalled in prophase 1

Menstrual cycyle selects one primarty oocyte to complete meiosis 1 each month

Spermatogenesis:

4 functional sperm cells per meiotic cycle

lifelong process