DNA & Chromosomes

DNA & Chromosomes

3.4.1 DNA, Genes and Chromosomes

Multiple Choice

What is the monomer of DNA?

• amino accid

• monosaccharide

• nucleotide

• fatty acid and glycerol

Multiple Select

What are the parts of a nucleotide?

• phosphate group

• nitrogenous base

• sugar

• amine

Multiple Choice

What sugar is found in DNA?

• ribose

• deoxyribose

• trioxyribose

• oxyribose

Multiple Choice

Which base matches up with guanine?

• adenine

• cytosine

• thymine

• uracil

Multiple Choice

Two hydrogen bonds hold together which two bases?

• A & T

• A & C

• C & G

• G & T

Nucleic Acids

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information carrying molecules

DNA forms the genetic code that:

•Determines the type of organism

•Directs growth and development

•Determines protein structure

Nucleotides

Each nucleotide consists of:-

• pentose sugar (2 types)

• phosphate group

• nitrogenous base (5 types)

Sugar is either

Deoxyribose (DNA) or ribose (RNA)

Bases are

Adenine, Guanine, Cytosine, Thymine or Uracil (RNA only)

Bases

The nitrogenous bases of the nucleotides are joined together like the rungs of a ladder to connect the two strands of nucleic acid

Adenine always bonds to Thymine

Cytosine always bonds to Guanine

They are connected by hydrogen bonds- three H bonds between C-G and two H bonds between A-T

Multiple Choice

What would the complementary DNA strand look like to this sequence of bases?

AAT CGC ATC GTA

• AAT CGC ATC GTA

• AAU CGC AUG CAU

• TTA GCG TAG CAT

• UUA GCG UAG CAU

Eukaryotic DNA

Eukaryotic cells contain linear DNA that exist as chromosomes

This DNA is found in the nucleus

A chromosome is one molecule of DNA wrapped around proteins called histones

This DNA and histones are then coiled very tightly to form a compact chromosome.

Histone + DNA = chromatin

DNA must be associated with histones to form a condensed chromosome

Histones

These are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes

Histones are a group of basic proteins that associate with DNA and help the DNA to condense it into chromatin

Chromatin

In the nucleus, DNA is associated with proteins (histones) 

The DNA helix is tightly coiled around histones to form chromatin

A nucleosome consists of eight histones with 2 turns of DNA around it (146 base pairs)

Chromatin further coils to form solenoids which form loops and minibands

DNA is only visible when chromosomes condense during cell division

Prokaryotic DNA

In prokaryotic cells, DNA molecules are shorter and circular

It is not wrapped around histones and is not contained within a nucleus

Instead, it condenses by supercoiling

The DNA in a prokaryote is similar to the DNA found in mitochondria and chloroplasts

Prokaryotic DNA is not wrapped around histones

Multiple Choice

What is formed when DNA is wrapped around histone proteins?

• Chromatin

• Chromosome

• Nucleosome

• Nucleotide

Multiple Choice

How many histone molecules are in a nucleosome?

• 2

• 4

• 8

• 16

Multiple Choice

DNA in prokaryotes condenses by

• superlating

• supercircling

• supercondensing

• supercoiling

Poll

How do you feel about this topic so far?

• I've got it!

• I think I understand

• I need to go through it again

• Help!

What is a Gene?

A gene is a sequence of DNA bases that codes for a polypeptide or functional RNA.

Functional RNA molecules are RNA that carry out tasks during protein synthesis, other than mRNA e.g. tRNA, rRNA

The order of bases in a gene determines the order of amino acids in a polypeptide.

Genes

One amino acid is coded for by a sequence of three bases: called a triplet or codon.

A complete set of genes is called a genome.

A complete set of proteins a cell can produce is a proteome.

Every gene occupies a fixed position, called a locus, on a particular DNA molecule

A gene is a length of DNA that codes for a specific protein

Introns and Exons

Not all of the DNA codes for proteins or functional DNA.

Introns are non-coding sections of DNA.

They can be found inside and outside genes.

Introns need to be cut out of the gene during proteins synthesis so they don’t interrupt the protein.

Exons code for the amino acid sequence.

Introns are 'junk' DNA and do not code for the protein

Non-Coding Multiple Repeats

These are found outside the genes.

They are DNA sequences that repeat over and over again e.g. ATATATATATATATAT

They don’t code for amino acids

It is thought they control gene activity, such as where genes are turned on and off

Multiple repeats are found outside the gene

Alleles

An allele is a different form of a gene.

The order of bases is slightly different, coding for a slightly different protein.

Multiple Choice

Which of these does not relate to a codon?

• Three bases

• Called a triplet

• An amino acid

• Three amino acids

Multiple Choice

Non-coding sections of DNA are called

• Exons

• Proteons

• Neons

• Introns

Multiple Choice

A different form of a gene is called

• an allele

• a locus

• a proteome

• an intron

What are you like?

Earlobes – Lobed is dominant

Eyes – Brown is dominant

Hair – Brown is dominant

Tongue Rolling – Dominant

Cleft Chin – Dominant

Dimples – Dominant

Handedness – Right is dominant

Freckles – Dominant

Curly Hair – Dominant

Hand Clasping – Left on top is dominant

Hairline – Widows peak is dominant

PTC (bitter) Tasting - Dominant

Chromosomes

Human somatic (body) cells contain 46 chromosomes - 44 autosomes and 2 sex chromosomes

Gametic cells contain 23 chromosomes

Telomeres and centromeres are essential components

Centromere divides chromosome into 2 arms (p and q) and is where spindle fibres attach during cell division

Centromere location gives chromosomes their characteristic shape, useful for identification

Telomeres are found at the end of chromosomes and protect them from degradation

Multiple Choice

Two versions of the same gene are called

• Exons

• Histones

• Loci

• Alleles

Poll

Now how do we feel about this topic?

• Got it!

• Mostly there

• I don't understand!

Homologous Chromosomes

Homologous Pairs

Humans have 23 pairs of chromosomes.

Pairs of matching chromosomes are called homologous pairs.

These are the same size and have the same genes.

They have different alleles of these genes, found at the same fixed position called a locus. (plural loci)

Multiple Choice

How many chromosomes do human somatic cells have?

• 23

• 46

• 64

Multiple Choice

If the liver cell of a giraffe has 88 chromosomes how many chromosomes would its sperm cells have?

• 88

• 44

• 23

• 46

Multiple Choice

What is the name given to the point of a chromosome where to two 'arms' attach?

• Telomere

• Centromere

• Locus

• Allele

Multiple Select

Which of these are dominant traits?

• Tongue rolling

• Cleft chin

• Straight hair

• Blue eyes

• Freckles