Lecture 5A - DNA and RNA Page Lecture 5B - Packaging DNA into the nucleus Page Lecture 5C - Human chromosomes, genes and alleles

What are nucleic acids?

DNA and RNA; molecules that store and transmit genetic information

What are the two types of nucleic acids?

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

What is the role of DNA?

Stores genetic information; directs its own replication; directs RNA synthesis; controls protein synthesis

What is the role of RNA?

Can carry coding information; structural roles; regulatory roles

What are nucleotides?

Monomers of nucleic acids

What are the three components of a nucleotide?

Ribose sugar; phosphoric acid; nitrogenous base

What is the role of ribose sugar?

Structural component; determines direction (5’ to 3’)

What is the role of phosphoric acid?

Structural; forms backbone; carries negative charge

What is the role of nitrogenous base?

Informational; determines genetic code

What is ribose?

5-carbon sugar in RNA

What is deoxyribose?

5-carbon sugar in DNA lacking oxygen at carbon 2

How do DNA and RNA sugars differ?

RNA has OH at C2; DNA has H (no oxygen) at C2

What are purines?

Adenine (A) and guanine (G)

What are pyrimidines?

Cytosine (C), thymine (T), uracil (U)

Which bases are in DNA?

A, T, C, G

Which bases are in RNA?

A, U, C, G

What is a nucleoside?

Sugar + base

What is a nucleotide?

Sugar + base + phosphate

What is the anomeric carbon?

Carbon where base attaches (1’ carbon)

What are 5’ and 3’ carbons?

Carbons in sugar that determine strand direction

Why is DNA negatively charged?

Phosphate groups are negatively charged at physiological pH

How are nucleotides linked?

Phosphodiester bonds between 5’ phosphate and 3’ OH

What direction are DNA/RNA strands built?

5’ to 3’

What is a DNA double helix?

Two antiparallel strands forming helical structure

What does antiparallel mean?

Strands run in opposite directions (5’→3’ and 3’→5’)

What holds DNA strands together?

Hydrogen bonds between complementary bases

What base pairs occur?

A-T (2 bonds); G-C (3 bonds)

What are major and minor grooves?

Regions in DNA helix important for protein binding

What is a gene?

Segment of DNA that codes for a functional product

What are exons?

Coding regions of a gene

What are introns?

Non-coding regions removed during RNA processing

What is a promoter?

Region controlling gene expression (upstream)

What are UTRs?

Untranslated regions at 5’ and 3’ ends

What is the start codon?

ATG (codes for methionine)

What is a stop codon?

Signals end of translation; does not code for amino acid

What is the poly A signal?

Signals addition of poly(A) tail to mRNA

What is a prokaryotic genome?

Small; circular DNA; no histones; no introns; no nucleus

Where is prokaryotic DNA located?

Nucleoid region in cytoplasm

How is prokaryotic DNA organised?

Folded and supercoiled loops

What is a eukaryotic genome?

Large; linear chromosomes; contains histones; contains introns

Where is eukaryotic DNA located?

Nucleus

How are transcription and translation separated?

Transcription in nucleus; translation in cytoplasm

What is chromatin?

DNA + histone proteins

Why do DNA and histones interact?

DNA is negatively charged; histones are positively charged

What are histones?

Proteins rich in basic amino acids (lysine, arginine)

What forms a nucleosome?

8 histones (2x H2A, H2B, H3, H4) + DNA wrapped around

What is linker DNA?

DNA between nucleosomes

What is histone H1?

Helps form 30 nm fibre

What are the stages of DNA packaging?

Helix → nucleosome → 30 nm fibre → looped domains → condensed chromosome

When are chromosomes fully condensed?

Metaphase

What is a chromosome?

One molecule of double-stranded DNA

What happens after DNA replication?

Two sister chromatids form

What are sister chromatids?

Identical copies of a chromosome

What are homologous chromosomes?

Pair of chromosomes with same genes (one from each parent)

What is a centromere?

Region joining sister chromatids

What are telomeres?

End regions of chromosomes

How many chromosomes in humans?

46 in somatic cells

What are autosomes?

22 pairs of non-sex chromosomes

What are sex chromosomes?

X and Y

What is female genotype?

XX

What is male genotype?

XY

What is diploid?

2 sets of chromosomes (2n = 46)

What is haploid?

1 set of chromosomes (n = 23)

What cells are haploid?

Gametes (egg and sperm)

What is mitosis?

Cell division producing identical diploid cells

What is meiosis?

Cell division producing haploid gametes

What is a karyotype?

Display of chromosomes in metaphase

What is cell communication?

Process by which cells detect and respond to signals

What are ligands?

Signalling molecules that bind receptors

What types of ligands exist?

Proteins; peptides; amino acids; steroids; gases; fatty acids

What are the three stages of cell signalling?

Reception; transduction; response

What happens in reception?

Ligand binds receptor

What happens in transduction?

Signal relayed through cascade

What happens in response?

Cellular change (gene expression, division, etc.)

What is endocrine signalling?

Hormones travel through bloodstream; slow; widespread

What is paracrine signalling?

Local signalling to nearby cells

What is autocrine signalling?

Cell signals itself

What is synaptic signalling?

Neurons release neurotransmitters across synapse

What is contact-dependent signalling?

Cells communicate via direct contact

What are receptors?

Proteins that detect signals

What are ion-channel receptors?

Open/close channels upon ligand binding

What are GPCRs?

Activate G-proteins and signalling cascades

What are enzyme-linked receptors?

Activate enzymes upon ligand binding

What are intracellular receptors?

Inside cell; bind hydrophobic ligands

What is signal amplification?

One signal triggers large cellular response

What are second messengers?

Small molecules that relay signals (e.g. cAMP)

What determines cell response?

Type of receptor and signalling pathway

Why can same ligand give different responses?

Different cells have different receptors/pathways

What is differentiation?

Process by which cells become specialised